Banning someone because they vehemently disagree with you? I mean, that's the only thing I can parse from their statement. It's basically saying, "I do not wish to discuss things with you, so you are banned".
The funny thing is, I don't think that's inherently wrong. In any group, I think you should be able to choose your friends. If you don't want to hang out with someone, then that sucks for that person, but lots of things in life suck. However, banning the co-founder because you no longer wish to talk to them is pretty much the definition of a power grab ;-)