Saruman basically spent centuries slowly spiralling downward to get to the point where he then openly declared himself and began doing things like locking up White Council members and breeding orcs.I always think about Saruman, who seemed to fall crazily quickly. I mean, the guy is planning to betray Sauron, but seriously, raising an army of Orcs is a pretty unambiguous sign that something's gone wrong with you morally.
Thingol basically regarded humans as scum. Hell, he regarded most of the Noldor as scum too.If I recall correctly, Tuor spent some years living in Gondolin and Turgon had a chance to get to know him pretty well before consenting. Elrond, of course, knew Aragorn well, Thingol and Beren... not so much.
He then changed his attitude and... well, Turin. So maybe it would have been better if he'd stayed hating them