Def. Sea change or sea-change is an English idiomatic expression which denotes a substantial change in perspective, especially one which affects a group or society at large, on a particular issue.
Some time ago I wrote an opinion piece titled: Dirty Words: Smoker, Vaper, Harm Reductionist? In the article I expressed my frustration that in government and NGO leadership circles publicly embracing harm reduction policy in the U.S. was still politically dangerous. Unfortunately, demonization of smokers, vapers or clean needle exchange programs is more likely to resonate with the public than nuanced discussions of proportional risk or the benefits of tobacco harm reduction strategies.