It isn't about thought control -- there's a whole big web where you can post what you want, so it's not even about freedom of speech.
It's about this site. This site is for people to ask for help or advice, or to ask those interesting questions that are hard to find answers to on the web (Why aren't humans furry? Why do I poop at the same time every day? Why don't we say 'onety-one'? -- to mention a few I've seen on here).
Hence the Guidelines for use of this site (see link, bottom of page).
If the Guidelines (you agreed to, btw, when you signed up for this service) aren't enforced, then the site fills with spam, porn, chat, hate, and other sludge.
People who have the kinds of questions this site was intended for, and people who can give good answers to those questions will come, see a lot of cr*p, and take their interesting questions and their knowledge elsewhere.
This site will have lost its purpose.
Hence, the Abuse Report system.
It's not for reporting things you disagree with, it's for reporting things that violate the guidelines (insults, spam, non-questions or answers, etc.).
It's about preserving this site as a safe place to ask questions, and a place to find interesting questions to answer.