Oh, I don't like or agree with democracy much at all. But that's not really relevant, the forums run on it, and I am able to use and respect the system regardless of what I think of it.
In democratic countries, do you vote on each decision the government makes, or do you vote to choose leaders who are capable of making those decisions on behalf of their country?
In the case of someone who is merely disruptive, but not at all delusional, or delusional but not at all disruptive, or many other cases, a referendum may well lead to a ban that ignores the rules based on the feelings of the members who happen to be actively posting at the time, members who may have a strong bias against a person simply because their beliefs clash in some way. It is better, because of this, to appoint calm, and objective persons who are capable of withholding personal bias and feelings to make such decisions, and to provide them with a clear set of rules to abide by. If both the rules and the moderaters are chosen by the community then the community has quite directly, and democratically, already made their decision, and the moderater simply ensures that the rules are objectively carried out.
Yes, the moderaters are just people, and they make mistakes just like everybody else. It is not whether they are perfect, but whether we trust them to make good decisions, and to admit and correct their mistakes, that is important.