I dunno... I think there are still plenty of polite, courteous people out there, the only problem is that we seem to only notice the ones that stand out as not being so. I learned this when I was doing a lot of cycling--a hundred cars will pass you with a wave, a smile, and plenty of breathing room, but you'll remember that one guy who crowded you into the ditch on a blind curve with his horn blaring. Once I made that connection and made an effort to notice the polite ones, they sure seemed a lot more common than they had before.
I know it definitely does my blood pressure a world of good to pay closer attention to the nice people. The only thing I can do is live by example and hope it rubs off on a few.