Despite all the good reasons for downvoting posts or comments, don't we think that upvoting quality content should be a priority?
I have seen plenty of posts that imo deserve a significant upvote but don't get any. If we support those, especially in the early stages of establishment, the long-term impact will be far greater.
I also question the mob/crowd tactics. Is it fair to flag up people and ask others to downvote? It may be straightforward in some cases, but in others, who knows? The examples listed are blatant (and justified), but not all I them may be.
It makes more sense to me to have a cleaning service (as proposed) that can downvote on posts in a transparent way. This will only be fair if it is driven by the community and has transparency. That would also allow for an educational element (I believe in educating members first before handing out punishment) that would retain community members (by being welcoming) and improve quality overall. The SteemStem community is a nice example I think.
Anyways, these are my 2 cents. In short, I support action on bad actors but we may have to organise ourselves to ensure fairness and positivity.