If you want to see a forum that has deliberately refused to implement a ratings system, go look at Something Awful, and weep.
Without a rating system, the only way to indicate that you like/dislike or agree/disagree with a post is to reply to it saying "I agree" or "This post is bad." Those sorts of posts are now 90% of all posts on SA (the others being a drunk Lowtax begging for Ambien money). You still get brigading and dogpiling, but with autistic walls of text rather than a bunch of little symbols. It's fucking terrible. They made emptyquoting bannable, but that has led to masses of white noise posting, where every sped on the site has to say something every time they agree with something else, no matter how irrelevant or uninteresting.
It also enables those with the time and autism to type those walls of text to look like they are in the majority, whereas in fact they were only the ones triggered enough to reply. The lack of a post rating system has thus been a major factor in SA being taken over by raging NEET troons, who dogpiled posts they disagreed with. Even though they started off as a tiny minority of posters, they made the majority of the posts (due to severe autism and unemployment), causing the moderation to swing their way because it looked like the site had a culture and political consensus that was in fact only that of a minority. I'm pretty sure that's what caused the downfalls of NeoGaf and ResetERA as well, where a small minority of lunatics with time on their hands took over the site by sheer weight of posting.
Removing a post rating system is not an effective way to prevent dogpiling or brigading. Posts will always be a popularity contest. I think KF/Xenforo does the best job I've seen with post rating, by giving some indication of why you like/dislike a post and keeping things public. Compare that with, say, the Cracked forums that had an anonymous post voting system that people wrote scripts to exploit, meaning that if you upset someone your "karma" would nosedive and you would have no idea why. Also the post rating system here gives just enough of an endorphin hit when someone gives you a positive rating without actually meaning anything mechanically, as opposed to Reddit, where unpopular posts can be sunk out of existence. It's the closest I've seen to a system that keeps everyone honest and rating in good faith.