If it's anything like War3 Banlist then it's not as harsh as you guys imagine. If someone has banlisted a certain player you get a warning, possibly with a reason. IF multiple persons have that one banlisted (not sure what the cap was) you can allow the tool to kick them, or warn you of that. THat's about it. It's so people HAVE some accountability when they join the game just to quit when they get killed the first time they try to attack a group of3 heroes. Or are generally being an ass, or staying in the game but doing nothing for 5 minutes!
The wc3 banlist was a bit of a clusterfuck. I ended up deleting all my "publicly uploaded" records and only use my friends ones. Too many times people are banned even though they did nothing wrong.
And in a casual game like this, you can expect the general competency level to not be as high as DoTA. Thus, you're going to have an extremely divided community which is probably not a good thing.
If there needs to be one of these "lists", a whitelist is much better. That way, people aren't punished for not playing well enough, or leaving for valid reasons, etc.