I use Tor to visit Facebook because I have to bypass some proxies.
The point is, I can access it without any problem, and my identity on Facebook changes according to the exit node. But when I visit any other site, it promotes a human-authentication method (image selecting or a captcha), and it doesn't work most of the times.
So, where is the problem? Are the other sites providing more identification security than Facebook? Or is Facebook not bothering with Tor and other access attempts that might be from bots?
And from a security perspective, what's the connection between bots and Tor activities?
Edit: as mentioned in comments, my evidence to support the assumptions is this:
every site rather than the Facebook is treating me as a bot activity, meaning that I receive a captchas, pictures selection and others to confirm "I'm human". So there is something in Tor activity that is similar to robotic activity, at least from those sites perspective!
And as for suggesting to use Facebook onion hidden service: I'm using Tor to bypass my local proxy, not to hide my id from ISP or other reasons.