How is this different from gay people hating on bisexual people? If you don't want people shitting on your identity don't erase and ridicule the identity of others.
It honestly bars down to that single line for that user. Experience within the community is so important for anyone within the lgbt community. It gives you a whole new understanding of the people, and yourself, as it shows that you both know. I remember for about a year or so before I came out of the closet (I came out when I was 14, so when I was around 12 and 13, I used to show resentment towards the community, obviously as a sign of self-resentment, but no one knew that. Not everyone will go through that exactly, but like a lot of subjects to do with other humans and their feelings/emotions, before stating facts, experience is a must to back them up imo.I'm nonbinary -- "genderfluid" is kind of a better idea but that's still often a class of NB -- and I can safely say you're full of **** on this one. I mean, I think the main point has been explained to you already, but:
How do you know that the NB/agender people you meet don't have dysphoria? Or that all of the trans people you've met have some class of dysphoria? Seriously, I think you're bending the truth about this one a little. Also the last thing does not apply solely to NB/agender people in "more extreme circles" (i.e. something I have pretty much only seen on Tumblr, the closest thing otherwise that I could possibly think of are trans-erasing radical feminists).
If these are your only experiences, you need more experience. Simple as that.