I think trans identities are usually tied into mental illness.
I think displaying a sign saying that at a Pride event is unnecessarily offensive and entirely ineffective (possibly counterproductive) in solving anything.
It's like holding up a sign saying GOD DOESN'T EXIST at a Christian funeral. There's a time and a place for such sentiments and this isn't it.
There does seem to be a bit of a double standard here with the kinds of placards the trans lot get away with, but I'm not confident that the arrest was out of place.
On the other topic, let's not be thick (/propagandistic) and pretend everybody who is opposed to what Israel are doing is a perfect little saint who couldn't possibly do anything bad.