People can be banned**. Trolls cannot. And you won't like or agree with everyone or even most people, particularly considering that they come with different personalities and from various cultures.
Since these forums are not operated to conform to one person's wishes and desires or definition of troll/racist/sexist/MEAN you must take responsibility for you own experience here and:
1. Engage them in discussion.
2. Ignore them.
You can ignore someone by the simple exercise of willpower, or by adding the person to your ignore list. I can't help you with the former, but for the latter, please see the directions in the default forum FAQ.
**And we don't do that except for spammers/illegal content that is not removed after notification and where we happen to notice that multiple accounts from the same user.