While I understand what people are saying about sitting out, I totally agree with you. Most of the time people "hurt themselves" when they get a big stacks. They simply get tired, bored, ect.. and get into pots they shouldn't be in. When in large field tournaments with slow blinds I have no problem sitting out for an hour, and I do it frequently. I'm just not going to lose that many chips.
Contrary to what is posted above, this is actually done frequently live. You often start with large stacks and there are very slow blinds. It is not uncommon to take long breaks. Go to the bathroom, take a smoke, get a drink, stretch your legs, maybe even get something to eat. I am going to be far more effective being "fresh" and having a few less chips than playing straight for 6-8 hours.
I would suggest that rather than "blind out" you step back in the game at some point, but I don't see a problem with long absences.