Some people don’t like more passwords and logins and signups and such. We get it.
Please be aware that logging in with different services may lead to duplicate accounts. In short, the system attempts to associate accounts with email addresses. If you have the same email on all of your accounts, then you can log in from any of them and everything should be fine. If you have different emails attached to Twitter and Facebook and Google and a custom Feralculture Username/Password, you could end up with 4 accounts.