I've notice that Interpersonal Skills Stack Exchange has a custom post notice which moderators can add to questions:
Controversial Post — You may use comments ONLY to suggest improvements. You may use answers ONLY to provide a solution to the specific question asked above. Moderators will remove debates, arguments or opinions without notice.
We have frequently encountered this problem on this website, too. Someone posts a question about a politically controversial topic. A few hours later there are 20+ comments of people fighting a flamewar about the subject matter of the question, while comments which actually seek to provide constructive improvement of the question itself get drowned out. And when you then scroll down to the answers, you see a couple answers with voting scores ranging from -3 to -10 which contain long rants about the subject of the question without answering the question itself, also with opinionated comment debates below them.
Please note that the above notice is just a synopsis of what the help for the commenting privilege says comments should be used for. It doesn't change anything about the rules for comments. It is just a reminder that these rules will be enforced.
That's why I think that we should also have that post notice text on Politics Stack Exchange.
What do you think about this?