Brian,
I think that bad sound stems from two things:
1) There is a natural tendency to adjust the sound with your eyes, rather than your ears (and ears need to be trained-- most people don't have a good idea what things should sound like).
2) There isn't really all that much proper pedagogy around being a sound man (and what there is is wrong on a lot of counts!). Many of the whys of doing things a certain way are not only lost to antiquity, they are wrong.
Let me give a great example:
In downtown Bellevue, they have a live concert series over the summer. They have an extensive PA system-- JBL mains and subs, big power amps, etc.
What always kills me?
They put the subs at either side of the stage. They comb filter like crazy, to the point that you can walk 1 foot into one of the comb filter areas, and the bass just... disappears. Of course, you're supposed to put the speakers on either side of the stage, for stereo, right? Wider dispersion? Bzzzt. Wrongo. But everybody does it. Never mind the sound! Everyone does it!
I won't even start in on shrieking tweeters pawned off as crystal clear highs.
I guess sound men are like drummers: it takes a pretty good one to be better than none at all.
Bradley