Hah, I can't tell you how many times I've had an argument with "less refined wheelers" (rednecks) or seen tires off of the same's trucks that have no tread in the middle because of this subject.
NO YOU SHOULDN'T RUN 50PSI IN YOUR 38" HAWGS JUST BECAUSE THE SIDEWALL SAYS SO!
It's not uncommon to find someone selling a set of offroad tires in Michigan with something in the description like, "center tread worn, good side lugs."
The funny part is there's a discussion on the Yahoo Groups Grand Vitara forum about guys running 35-40psi in their 28-30" tall radial tires.  I told them they were nuts, I was running 25psi in mine and probably should be a pound or two less.  They talked to me like I was ignorant.  I bet their side lugs aren't even touching the ground!