Comments should be removed if:
- they mention an entity's name and therefore infringe upon privacy or are slanderous or potentially libellous
- if they are off topic
- if they are profane, racist, sexist, homophobic, etc
- if they otherwise contravene your terms of service or rules of engagement on the site
- if they are in another language and your site is explicitly built for one specific group of localized users

These are common sense rules. People don't just get to remove comments if their views or affiliations change. That said, if you accept comments on your site you also accept responsibility for the content. This included your content or content generated by your community. There's a bigger reputation at stake at all times, and that's yours!