Paraphrased from above and other threads, since you did not read them.
I wont go into detail, but IP ban is not always possible. The idea is to have as many possible ways to ban as you can, and implement those that fit the situation best.
As for free ones. I have several reasons..
1. people forget them, then they are terminated. Sending email back and forth saying it is diconnected
2. people make multiple accounts
3. free email companies not only come and go, but provide shitty service. Hotmail in particular. How many times has it been down recently? When they are down all email comes back. Which triggers a program on Bg to change the account to awaiting email confirmation.
Gmail
Some people have no issues with it, in the end, it is now just a free email service, and has already been abused, BADLY.
Forcing people to use an email that can be traced to them makes them more responsible. People feel the net is anonymous, and it is far from it. It has built in caller ID. By making people know they can be held accountable, it keeps A LOT of the riff raff off of BG. Trust me, it has cut down a ton. Most people who want to mess witha website almost always use a free email provider. Making them use a legit, traceable IP makes it easier to get them into troubl should they actually do something wrong as well.
Most importantly, it is not hard to get one from your internet provider.
If you cannot handle or deal withthat, sorry, go someplace else. Doing this has cut down on over half of the crap that was happening here.