I don't think it's helpful to pin the blame on one demographic of people over another. I happened to run a guild with """tumblrina""" rules like "don't use slurs" and "don't make racist jokes", and we had this exact kind of issue, people trying to spread rumours and making level 1 alts to try and make us think it was more than just them... from people who were kicked for breaking them. The "rumours" were along the lines of that we were a guild of over-sensitive SJWs and that I was a dictator with "oppression privilege". Because these people were mad that I'd told them they couldn't stay in our guild if they kept breaking the very clear rule we had about slurs and didn't stop calling things r*t*rded.
And of course they tried to use this image against me - paint me as a hysterical child who was "triggered" by the tiniest thing, and therefore couldn't possibly run a decent guild. It was all bollocks, and it never stuck, because at the end of the day our guild was decent, openly, and added a significant amount of value to the RP community with our presence. But that didn't stop the attempted harassment campaigns. I think it took the most tenacious of them a year (and some actual, legit, not-sure-in-retrospect-why-I-didn't-call-the-police stalking of me personally) to give up.
Point is, people like this - who start a harassment campaign when you tell them to leave - exist in any cross-section of any community you sample. You can't afford to think that all the people in your group will be reasonable when crossed just because you happen to agree with them on other matters, like politics or game lore.
As for how to deal with it:
1. Don't give them a rise. Don't get upset at them. Don't reply to the level 1 alt tells at all. Blacklist the original person who caused the issue, if you haven't already. You are not obligated to entertain this. If your members bring it up, address it with them in a calm, transparent way. Say that such-and-such a member was kicked for [reason], and then these rumours began. Tell them they're free to ignore the level 1 alt if it's causing them distress. Tell them if they have any concerns about the way the FC is run, they're free to bring them to the officer team as per usual (and then address them in the usual manner you do, which I hope is open and considerate). And if an outside player asks you, you're not obligated to either prostrate yourself to them or to give them details. Tell them you would hope people would witness your FC first-hand before believing bad things about it, and then change the subject. Think twice about recruiting this kind of person - if they can believe bad rumours about you now, what of later?
2. Don't change your FC's behaviour. Barring simple and non-loaded things like locking an FC house to non-members, you shouldn't change the way you run your events, interact with the wider community, or advertise for recruitment. Changing these things teaches the person that if they want to stop you from, say, openly recruiting for your FC, all they need to do is create 3 level 1 alts and send you /tells doubting your leadership. So next time they want to change something about your behaviour, they'll create 3 more alts. Remember that, at the end of the day, you have very little evidence these rumours are actually rumours. Treating them like they're real makes them more real. Don't give this person the satisfaction. [This differs from advice when it comes to IRL stalking, because online, there's no actual physical danger involved in just continuing about your business.]
3. Don't be afraid to get the GMs involved if things get out of hand. The GMs in this game take stalking and harassment very seriously. Privately collect the names of the level 1 alts who send you /tells about this (blacklisting them is a good way to do this automatically, especially if you don't have many other people on your blacklist). If it keeps up for too long (honestly the fact you're writing to us today tells me you're already fed up), gets worse, or the messages get at all threatening, file a GM ticket. They'll tell you what they can do and help you out as best they can. And if you happen to get an unhelpful GM, file again, as you'll likely get a different member of staff handling your ticket - though I've honestly never heard of someone having problems with the GMs with regards to harassment. Compared to the GMs in WoW, the ones in XIV are pretty clued up on problems like this.
Good luck. I also want to emphasise: this is not your fault. It's not your fault and it's actually not your job to handle it, even though you more or less have to. This person is being horrible by doing what they're doing, and that's on them, not you. If you want to know whether you're running the FC well, look to yourself and what you're doing - not to reviews on random websites, and not to the words of level 1 alts who may or may not belong to someone who feels unduly slighted and has nothing better to do than to try and turn that feeling back on you.
And of course they tried to use this image against me - paint me as a hysterical child who was "triggered" by the tiniest thing, and therefore couldn't possibly run a decent guild. It was all bollocks, and it never stuck, because at the end of the day our guild was decent, openly, and added a significant amount of value to the RP community with our presence. But that didn't stop the attempted harassment campaigns. I think it took the most tenacious of them a year (and some actual, legit, not-sure-in-retrospect-why-I-didn't-call-the-police stalking of me personally) to give up.
Point is, people like this - who start a harassment campaign when you tell them to leave - exist in any cross-section of any community you sample. You can't afford to think that all the people in your group will be reasonable when crossed just because you happen to agree with them on other matters, like politics or game lore.
As for how to deal with it:
1. Don't give them a rise. Don't get upset at them. Don't reply to the level 1 alt tells at all. Blacklist the original person who caused the issue, if you haven't already. You are not obligated to entertain this. If your members bring it up, address it with them in a calm, transparent way. Say that such-and-such a member was kicked for [reason], and then these rumours began. Tell them they're free to ignore the level 1 alt if it's causing them distress. Tell them if they have any concerns about the way the FC is run, they're free to bring them to the officer team as per usual (and then address them in the usual manner you do, which I hope is open and considerate). And if an outside player asks you, you're not obligated to either prostrate yourself to them or to give them details. Tell them you would hope people would witness your FC first-hand before believing bad things about it, and then change the subject. Think twice about recruiting this kind of person - if they can believe bad rumours about you now, what of later?
2. Don't change your FC's behaviour. Barring simple and non-loaded things like locking an FC house to non-members, you shouldn't change the way you run your events, interact with the wider community, or advertise for recruitment. Changing these things teaches the person that if they want to stop you from, say, openly recruiting for your FC, all they need to do is create 3 level 1 alts and send you /tells doubting your leadership. So next time they want to change something about your behaviour, they'll create 3 more alts. Remember that, at the end of the day, you have very little evidence these rumours are actually rumours. Treating them like they're real makes them more real. Don't give this person the satisfaction. [This differs from advice when it comes to IRL stalking, because online, there's no actual physical danger involved in just continuing about your business.]
3. Don't be afraid to get the GMs involved if things get out of hand. The GMs in this game take stalking and harassment very seriously. Privately collect the names of the level 1 alts who send you /tells about this (blacklisting them is a good way to do this automatically, especially if you don't have many other people on your blacklist). If it keeps up for too long (honestly the fact you're writing to us today tells me you're already fed up), gets worse, or the messages get at all threatening, file a GM ticket. They'll tell you what they can do and help you out as best they can. And if you happen to get an unhelpful GM, file again, as you'll likely get a different member of staff handling your ticket - though I've honestly never heard of someone having problems with the GMs with regards to harassment. Compared to the GMs in WoW, the ones in XIV are pretty clued up on problems like this.
Good luck. I also want to emphasise: this is not your fault. It's not your fault and it's actually not your job to handle it, even though you more or less have to. This person is being horrible by doing what they're doing, and that's on them, not you. If you want to know whether you're running the FC well, look to yourself and what you're doing - not to reviews on random websites, and not to the words of level 1 alts who may or may not belong to someone who feels unduly slighted and has nothing better to do than to try and turn that feeling back on you.