Exactly. Common ground. Instead of suspicion and guesses, you don't act to harm some ones ratings without a review of evidence. I would say the best way to do it frankly would be to present any evidence of theft, violation of contractual agreement, or violation of applicable laws to the community in the scam accusation area, then allow others to review it. If the evidence presented is sufficient naturally people will want to negative rate them.
I disagree with you here. Many scammers rely on pulling in as many customers as possible over a short period of time, before they are exposed. If we require every suspicion to be first posted, and then wait for the community to review before tagging, you are now giving them an extra 24-48 hours to continue scamming until they get tagged. It also simply isn't feasible to start a new thread and have a discussion about every suspected scammer - the board would be overrun with new threads and being a DT member would become a full time job to read and review every accusation.
I think your method is correct and workable in marginal or uncertain cases, but these are the minority. Trying to apply this to every case would rapidly overload the system.
Does Theymos currently run around enforcing the "guideline" that it is not acceptable to leave ratings for disagreeing with people's opinions every time some one does this? No, of course not. People point out to them that it is not acceptable and either they change it or they lose their own reputation and or are excluded. You can have both, because we already have both.
Fair point, which I accept. However, you seem to be arguing against yourself here. Many DT users pre-emptively tag account sellers, Ponzi promoters, loan requests with no/fake collateral, fake ICOs, etc, before they are successful in their scamming. By your metric, none of these people would be tagged until after they had scammed and there was evidence of theft. Now, if the community decided this was "not acceptable", as you put it, then the users who leave these ratings should be "losing their reputation and/or being excluded". This isn't happening, so the only conclusion is that a majority of the community supports this position. You, of course, can completely disagree with this stance, but as theymos has more-or-less made DT a democracy, the majority view wins.
I agree with you that we shouldn't be tagging people for disagreements or differing points of view, but I disagree that we should be waiting for evidence of a scam being successful before we tag the scammers. I also don't think theymos just giving a top down declaration, but leaving the system as is - inclusions and exclusions based on community votes - would actually result in the change you are looking for.