One can argue lots of things, but I think it's a crucial support network for people not near lots of like-minded others. What "real life" peer group is a trans kid in small town in Kansas supposed to hang out with and get support from?
I worry for what transpeople -- who lack meat-world social choices -- are enticed to reveal about themselves online to the secret police. Our governments' thugs are happy to lend an unsympathetic ear to their problems.
One mitigating factor, though, is that there seems to be a wider disconnect between Mastodon IDs and real life IDs than there is between real life and Twitter. I have plenty of Mastodon friends who could be sitting at the next desk as I type this for all I know. Also, having multiple Mastodon accounts is seen as a perfectly normal and acceptable thing to do, so @joe@joefamily.name might post vastly different stuff than on their @jane@transfriendly.social.