Most of the forums I mod are based around DIY and home improvements. The experts on them go on to freely offer advice to the general public and generally be helpful without expecting kudos or reward. (Thanks and feedback are always appreciated though).
On one forum we have about a dozen mods looking after over thirty thousand registered users with probably 500+ regular contributors, so the opinionated fools get either diluted or drowned out.
We have our general discussion areas, but because we're national - and often international - we don't tend to get bogged down in local partisan political spats. And when we do have a "frank exchange of views" on a national subject like immigration, terrorism, or the EU, at least we have a degree of mutual respect based upon the expert advice we have all freely given to others.
We as mods are also plenty willing to issue warnings, suspensions or bans to users who consistently drag threads off topic, abuse others, or state untruths as facts. As the site owner often says, "You may think this is a democracy, and we here are easy going enough that it often appears to be. But as long as I'm paying for the server space, in the final analysis - my word is law!"