Emailing with yet another guy I used to work with a long time ago, the question of why he should use Facebook comes up. I sent him a pointer to my long-winded personal piece, but then realized it could be a lot shorter, when talking to another developer.
You probably have another active 20 or 30 years as a developer (I know you say 10, but I'd bet you won't want to hang it up in 10).
The people you compete with, many will have grown up with Facebook, the way you grew up with cable TV.
It's just there, part of the environment. The fact that you remember a time before Facebook will be an advantage, but you can't let your competitors have the advantage of understanding Facebook and you don't.
That's why you're hurting yourself if you don't use it.