With reference to the OP, I know it's lazy, but I hope folks don't mind if I c & p something I just put on the "Feminists Aren't Man Haters" thread, as it relates to trolling behaviours.
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Yes, the difficulty is trying to tease out which folks are the "genuine enquirers" and which are the "bullshitters with an agenda," since they don't turn up with neat labels pinned to their jumpers and at first glance, can appear quite similar.
However, I don't think we should assume that "genuine enquirers" are all going to be shrinking violets, recoiling in fear if challenged or questioned about their approach in any way. I know, for example, I didn't join an anti-racist campaign organisation when I lived in London with the expectation that I'd be fawned over, or even "rewarded" for being a "good" white person, willing to support the rights of marginalised non-white people. I expected to hear things that would make me squirm, make me feel deeply uncomfortable but most of all, make me think and hopefully make me not assume that I was completely right about stuff. I also recognised that for many Black, Asian and ethnic minority people, their experience of engagement with white people has probably not been terribly good.
They'll have experienced ignorant, ill-informed comments, patronising attitudes, defensiveness, fear or even abuse. It's a big ask to think that they'll automatically assume that as a white person, I'm not going to be like that. I understand and fully accept that I need to "earn" trust and if it's not forthcoming, it's probably because I am saying or doing something wrong, not because they are "doing anti-racism" wrong.
So, imho, I don't believe those folks who are "genuine" in their support for a movement, or wanting to lend their support, are going to wail and gnash their teeth if someone dares to ignore them, question their comments, challenge their assertions or even suggest that they might be a troll. They'll understand that the frosty or unpleasant response they get isn't a patch on the real marginalisation, oppression and abuse that members of the group experience in RL and on message boards, just for being who they are. They'll be patient, they'll try and learn, they'll stick with it.
Yes, it's important to label the comments and behaviour without personal attacks, but there are bound to be some folks who can't (rather won't) recognise the difference - particularly those who are determined to feel offended and to whine that they are being silenced/judged/labelled/etc., when challenged or questioned (or sometimes even just not agreed with.) If they throw a hissy fit and/or leave, that was something they probably planned to do anyhow, so no skin off anyone's nose.