The most important reason these days, to allow players to have contact with OB during the throw, is simply to eliminate one more rule violation for the catty chatters to complain about.
That's a glib way of stating it, but I think it's pretty important.
If you can't tell whether a rule is being broken or not, then it's probably not a great rule. Are we supposed to be able to tell if a player lifts their back foot a millisecond before or after releasing the disc?
I've see plenty of players say "don't worry, I pick up my back foot before I release" but then when watching it on replay, they clearly don't. Players are already breaking this rule on a regular basis, but no one can call a violation because it happens too fast. If you just got rid of the rule, would it actually hurt anything?
I don't buy the dangerous stance argument. Your marker will still have to be in bounds. Your front supporting point will still have to be in bounds. If it's unsafe to put your back supporting point OB, then don't put it there; put it in bounds like normal.
(and yes, you can apply the same logic to the jump putt rules)