Because otherwise one could evade being convicted of OneTrueWayism by simply never making a general statement. Right?
I agree about the opinion vs. facts thing, too. One thing that irks me is when somebody states something as a fact, in a way that is dismissive/pedantic, and then when you call them out for it they say, "Well OF COURSE that's just my opinion."
This discussion involves both opinions and facts (or claims to facts, anyway), and the consistent contributors to this thread have all demonstrated competence with the English language. It's easy enough to express a thought as an opinion, so I will interpret apparent statements of fact as just that.