@Randomran: in my experience, the difference is always in behaviour. The user that edits without paying attention to others creates problems, the user that discusses and listens first doesn't create problems. Weather they are opinionated or not isn't particularly important: the disruptive guys aren't always the opinionated guys. I believe that when discussions follow the form of intelligent inquiry, consensus will eventually always shift towards higher quality (more neutral, more balanced). It's the contributors that prevent intelligent inquiry (by being rude, by editing against the consensus, etc) that form the real barrier.
I am opinionated in many subjects, so are all of us. Yet I keep that in mind when I edit, or simply don't edit the subjects I think I'm not neutral in.
Test case: use my behavior on here as a new user. (yes I am handing out darts)
I am opinionated.
I have done original research on brand.
I am vocal and I am also tenacious.
I have offended at least one person on this task force.
Am I disruptive?
Note: the brand graphic I posted is based on years of reading/research and on other people's work as well but it is not cited because for the most part it is common knowledge in my field.
What is different about me or my approach than users all of you would call disruptive?
Honestly, I'm not sure.
How offensive is it? Obviously "shut up!" or "you're an ass" is not civil behavior. But is it offensive that the new user saw something they thought was untrue and said "stop pushing lies on Wikipedia. I'm removing your lies." Is it offensive if the new user said adamantly "listen, I'm an expert on this, and you need to step aside"?
And how original is the original research? If it's blatant, then that's a strike against you. But what if there are lots of people on the Wiki who think it's fair game? An admin comes down on you... and like many "true believers" do, they pour into the discussion and overwhelm the admin. They point out that the new user used a press release, or an advertisement, or a polished but self-published website. You point out that this is still original research, and they no it's not, and "ignore all rules" anyway.
... you're going to have a hard time dealing with anything but the most obvious vandalism. What makes "true believers" so disruptive is that they think it's enough that they wrote some grammatical sentences that are on topic, and there are plenty of people who will say that's fair game.