One of the strengths of the SE system is that it puts tools into the hands of regular users that allow them to police the site without relying exclusively on moderators or other users with administrative privileges. The higher someone's reputation the more engaged they are with the community so the more tools they have available. The system has trust built into it. Your reputation shows (roughly) how much the system trusts you - both to supply good content and to police the site.
For example, all users can suggest edits to posts and once they hit 2,000 reputation make edits without peer review. This enables inflammatory parts of posts to be edited out - assuming that the rest of the post is valid and useful of course.
Nearly all users can flag posts "for moderator attention". This doesn't just bring the post to the attention of the aforesaid moderators but also adds it to one of the review queues where regular users can add their input into what should happen to the post. For certain flags - spam and rude/abusive posts - if enough users agree, the post is deleted automatically without needing any further input.
Additionally, as new sites can only* be created through Area 51 and only go public when there is sufficient interest. This means that there is a built in core of users who are quite heavily invested in the site and will be active in policing it to keep the quality high.
The focus of all SE sites are the questions and answers, not the users who post them. I believe that this reduces the opportunities for trolling as it's harder (but not impossible, alas) to target users.
When users are targeted there are scripts and procedures that spot the patterns and bring the actions to the attention of the moderators where we have the tools to check things out to see if we agree. Then there are actions we can take. Posts can be deleted and users (if necessary) can be suspended.
The suspension system works because it concentrates on the behaviour not the person and once the suspension is over the user is free to come back and participate in the community once again. Repeat offenders are dealt with more severely and may have their account removed.
* There have been a few sites (apart from the original three) that weren't created through the Area 51 process. Some were imports from the first time you could buy the system and install it yourself (MathOverflow), others were created for specific purposes (Patents).