So it's actually a lot better than it might appear - they're obviously familiar with what happens when anyone can edit an article on a contentious topic, and it would be a massive shit-show if it was as simple as "whoever's most stubborn at changing the topic to be the way they want it wins." I've been involved with editing a controversial topic, and I can say that as long as it's something that enough people care about, the system actually does produce something pretty close to an unbiased view.
There's a whole set of rules and guidelines, including some specifically for this situation, and there's a whole set of remedies with a gradual escalation, up from just getting other people involved to talk about things, all the way to IP or user-account blocking and banning if people don't follow what the rules are supposed to be.
I think where the system is lacking is for situations like this where someone's making edits "under the radar"; where it's a topic that not a lot of people care about, or where their edits are subtle enough that no one really recognizes that they're coming with a particular agenda. But in general, it's quite a good system which is the only reason Wikipedia isn't a big 4chan-esque vote-rigging dumpster fire.