Let's say you have 3 bets that are all 3-1 with +EV. If you make a $20 win bet on the first horse and win you will be betting 4 times as much on your second horse and if the second one wins you will be betting 16 times as much on the 3rd horse as you did the first horse. What would be considered idiotic money management if the bets were made outside of the parlay bet somehow become good for a bettor if done in a parlay?

Having +EV bets is only part of the equation when trying to win the other is proper money management.

I agree that parlays are stupid bets.

But it is ALSO stupid to want to hedge a +EV bet. In other words, if you really believe the last bet on the parlay is +EV, it is entirely superstitious to lose the courage of your convictions just because there is now a lot of money on the table. If you can't see it through, don't bet it in the first place.