Ideology to some extent is behavior, or at least helps determine behavior, when people act in a manner consistent with their own ideological positions. I can see an appeal to "allow all ideas as long as they don't make trouble", but when the nature of most ideologies is to include something along the lines of "it is a morally good thing to spread this ideology to other people" to a lesser or greater extent, and some ideologies require harmful behavior for one to act consistently with it, the conclusion that seems obvious to me is that believing in certain ideologies is itself bad enough behavior for it to be justifiable to exclude those people from a given online community, because such a person will either cause trouble or be a hypocrite. And after all, ideology isn't some immutable inherit trait, a person can change one's ideology and people often do.

All that being said, that particular statement isn't really a clear statement of ideology at all. I disagree with it's implication, but all it really does is demonstrate either a misunderstanding of what harm reduction means, or a viewpoint that is too black-and-white to allow for it, which can be a feature of too many ideological positions to narrow it down.