It may be a good tool for conscientious, rational people with a common goal of reaching truth or of outlining an argument. But as a crowdsourced website trying to actually come to consensus about specific arguments and refutations, it's mostly GIGO, which is to be expected from any website whose user community isn't strongly pre-selected.
If you look briefly at e.g the most heavily commented page on the site, for "there is no such thing as global warming", which lots of people evidently spent time on, you'll mostly update in the direction of "there's a big and very complicated argument about this with lots of points on both sides which the other side then claims to refute, ad nauseam". And if you take the time to actually read some of it, you'll realize it's a colossal waste of time that doesn't deserve the name of "argument".
This looks to be a very good example of the dangers of a little bit of rationality, or a little bit of intelligence. The layout encourages deploying Fully General Counter Arguments. There appears to be no mechanism to ensure the information on which the arguments are based is either good, or agreed upon.
I recently found out about arguman. It's an online tool to dissect arguments and structure agreement and refutation.
It seems like something that's been discussed about in LW some times in the past.