Can I just explain this real quick? No one thinks that this is offensive because cisgender actors are somehow "desecrating our good name" by portraying trans characters on TV or something (well, someone probably does, but they're stupid, so...), this is more about transgender actors who have a hard enough time getting work as it is without cisgender actors taking roles that one would think they'd be perfect for. This isn't a matter of finding the best person for the job, transgender actors aren't even being considered for these roles, and that's sort of the problem here.
If we only allowed trans people to play trans people, and cis people to play cis people, that would still come out to trans people getting more roles than they're currently getting.