That's just right. By signing up on a new website using facebook, I get all the downsides of facebook login (having to log into facebook, having them track me,

That's just right. By signing up on a new website using facebook, I get all the downsides of facebook login (having to log into facebook, having them track me, giving the website a bunch of personal data), and I still have to do the manual registration form. There are no upsides for me (except maybe not having to manually type my email address).