Seems to me like some users have arbitrary authority to convert other users' answers to comments, truncate comments, and ignore responses to comments. Is that true? If so, isn't that kind of like censorship? Who gets to make these determinations?
StackExchange is built an run by the users. They ask questions, give answers and vote on both. Upon voting users get reputation and earn privileges. Besides "normal" users there are administrators. They can convert answers to comments, delete things etc. The Tor.SE site has three moderators at the moment.
I don't know which answers you're talking about. But quite often new users don't have enough reputation to comment on posts. They often write a new answer, but really want to comment on a post. In this case the answer is moved to a comment.
Furthermore sometimes there are "me too"-answers. This means that a person answers "I have the same problem". This is also a case to move or even delete the answer.
In the end there are spammers which want to share their "valueable" sites. In this case posts are also deleted.
The site about moderators and their role has some more information. In the end it is the goal to have a good Q&A page where good questions meet good answers and provide value to the visitors.