I believe the guidelines are for trustworthy people and DefaultTrust. There were never any guidelines for non-DT members (for the old or the new system), you could send as many frivolous ratings as you've wanted.
Ok, then we disagree what is valid for DefaultTrust or not. I don't think red trust for trolling etc is a good use of DefaultTrust privileges.
I think I have to agree with someone who ditrusts my judgement and uses proper ways to show it using the trust list exclusion. It is fully logical that trust ratings should only be used if a person is high risk to trade, but not just if you think his opinion doesn't matches yours hence he would scam in future even if he would have not done it explicitly until.
Makeing the use of trust ratings more dynamic than it just being an indication of being high risk to trade with makes it open to "selective enforcement" as everyone thinks any enemy in thoughts is a bad person overall and risky to trade with even if he is not in doing transactions in reality.