I really agree with pretty much everything you're saying, but I wonder about the point you're making above...the idea of "social contagion" where Facebook is churning out trans people is pure BS of course, but I think social media has had a big impact in allowing trans people to spread their stories and that's been at least part of an increase of awareness/acceptance. For the X% of people who have been trans since long before we were using that word for it, this is just reducing the stigma for them to lead their lives as their true selves and that's nothing but a good thing.
Where I wonder if there's anything to the 'alleged uptick', is the idea that for kids who are growing up and trying to figure out who they are, they're likely to try on many hats in that search. These days, now that this is a more acceptable option on the menu, so to speak, will it lead to at least a perceived uptick of people experimenting with living life as trans while trying to figure themselves out?
I have no evidence of that happening and maybe I'm way off base, it's just what I'd assume is happening on at least some level.