There's an evil with social login in that you give up the knowledge of your social (presumably personal) network to random 3rd parties. That's even worse than email address. With password managers being essentially mandatory now, it's not too hard to create a new email/password based account for every new site. But recently I realized that I don't use my FB for anything. I have zero friends, don't allow friend reques…
Social login doesn't necessarily give up that much info. Your social network knows who logged in to. The third-party only gets whatever info you accede to which usually is just an email address or name.
The huge bonus to users and site owners is that that site isn't storing a password for you. It's easy to screw up password storage.