Becuase it will, in all likelihood, not be used with the "best of intentions".... that I am constantly assured it will be used for. It promotes division in the community, faux-griefing, and brings the community apart instead of together.
This is a very naive statement. I for one do NOT want to be part of the majority of the demi community because I know that a huge bunch of them are or will be asshats, just like in dota and many other online games for that matter. This is why a banlist is good so I can choose whom I do not want to play with.
For now, people in demi are deceptively polite compared to dota because this game has not become mainstream yet, players are hard to find so we have to "work along" to get a game going. When this game becomes mainstream and the community grows in number it will decline in quality. The community will become less polite, cordial and be filled with asshats - this is why banlist must be implemented so I can exclude all the tards that have spoiled my previous games. What the hell do you care, unless you are an RQ'er?
If you claim that it divedes the community then at least it does so in the right way - it splits the tards from the proper gamers.