I like your thinking

It doesn't make sense that trans people are hating on cis people. It's like should I be trans? Should everyone be trans? But you see, when everyone is trans, no one is.

Perhaps it was a hatred that was born from fear or frustration. Enough cis people not being educated enough to understand the struggle, or harassing trans people, and the community eventually grows tired of it. Soon, they associate cis with frustration, and lash out against those who feel associated with that label. Kind of like bronies or homestuck.

The thing is, though, on Tumblr, people forget that white cis straight middle class males didn't choose to be like that any more than black trans gay poor women chose to be like they are. It's hypocrisy at its finest.

Now you see the fault in tumblr and many othe places. Instead of everyone being treated equally it has become the opposite of how things used to be. Straights hated on, cis hated on, skinny hated on. You get the idea. (Not always the case but it is still an issue)