Extra principal question... partly answered

After a little asking around, it seems like most people I talk to recommend paying down the mortgage when possible. This is more so necessary the higher the rate you are paying. Paying your mortgage off slowly can have the side effect of encroaching on your retirement budget in the future if you still have a huge principal laying around. Let me see if I can find good arguments on the other side. Still, with todays home prices, it would be forever before your mortgage disappear, has anyone thought about that?