I had the same problem with another site and I was scared to get in more troubles since I had another one banned. So I just disabled google ads on it.
Fortunately, there are many different ad networks for many different publishers. Reddit is using Adzerk ... maybe they will work for you. There's also a bunch of ad networks that specialize in different areas, including porn, gambling, etc -- stuff that Google won't ever touch. You may still be able to use AdSense if you segment where the ad is shown in places where you're less likely to have negative UGC, such as non-UGC portions of your site or forum topics that are more moderated.
Any publisher can do this on their own. They can sell their own ad space at a premium, and use an ad network throughout the rest of the site -- it's called "remnant" inventory. If someone writes profanity or uploads something for that page, them switch the ads off, or use a different ad network that will tolerate that. High traffic sites frequently use multiple ad networks to maximize revenue yield.