Blacklist? How 'bout, make opinion into a kiss of death: Go through the questions so-tagged, and vote to close them. If they're already closed, vote to delete them. If they don't deserve either, then re-tag them.
Seriously, this is even more vacuous than "subjective". I have a lot of opinions, and varying amounts of objective support for them. Many of them are shared very widely, and I introduce some of them into all but the most objective questions (like "Is this valid according to the Standard?").
My opinion, which is only somewhat subjective, is that "opinion" is worse in every way than "subjective".