I know, I'm subscribed to many of their communities already, they are some of the nicest people I've met on the fediverse. If I was going to recommend my friends join Lemmy I would recommend they join lemmy.blahaj.zone. However even though there are good instances which are safe spaces it doesn't detract from the problem, since they will still use the federated general communities and thus will still encounter those problems. Even if they're on the friendly insances, the problem gets federated.
That's why it is important to address transphobia in the fediverse as a whole, having safe spaces help but we should expect a level of common decency in any community. Not just in the trans-specific communities.