Each moderator action reduces participation on the site, as the moment a user feels a moderator's presence, the user usually leaves.
The best policy is to ask the participants if the discussion is off topic, and if they agree, move to chat. If they disagree leave the comments alone, or let them delete it themselves. The quality of the site is not kept high by moderation, but by participation. The greater the participation, the higher the quality. A bad comment gets moderated by other users, not by moderators.
There has been no serious attack of low-quality comments anywhere on the site, and there is no need for new policy. This is simply an attempt to legislate away the problem of moderators stepping on users toes, by making rules which justify this.
The simple principle is this: everything you need to do on this site, you can do with the consent of the individual you are moderating. You hardly need to do anything unilaterally, or by imposition of community decisions on a user. A +3 voted comment is not enough, as a single user arguing with 3 other people who are wrong will get +3 on moving their comments easily.
If the thread is off topic, start a community moderation thread, and it will get votes if the discussion is really off-topic. But it won't get votes normally, because normally there is no problem.