no it is not and actually you can do it as much as you want spam-free!
No, you don't. You can only browser particular things (like photo albums) if a user invites you to by sending you a special URL. I think that sucks.
By sending friend invites.
No, it's not at the moment, it could be a scam in order to get your password.
You can talk to your friend on facebook by sending her a message, sending her a chat or posting on her wall.
Yes, Facebook does support evite sending. To send an evite via facebook, click "Post on Facebook" on the confirmation page of the completed evite invitation list.
just spam people. keep on sending them invites
No.
Invites were the thing when Gmail was born. Now you do not need invites to access Gmail. You can directly sign up and fill your details.
When you send a message on Facebook, you automatically get identified to the receiver.
You can stop someone by sending message only by blocking that person from your Facebook. Messages will only be stopped when you block the person who is stalking.
Honestly, it's because facebook chat is a load of bollocks. There's no reason but that.
Gmail was established in the year 2004. It is not a stable but beta version with invites. You could not join without someone sending you an invite.