re: Poker & Donking..why is it supposed to be bad?
Well, one negative is that you'll often miss out on picking up a cbet because the preflop raiser will just fold to your donk bet. Sometimes he'll flat your donk bet and wait to see how you play the turn. Other times he'll raise your donk bet leaving you with very little information about the strength of his hand as it compares to yours and you'll be guessing as if your hand is good or if you're miles behind.
Basically playing OOP always sucks but by donk betting you're generally making it suck even more. Now if you have a specific read that a player always raises donk bets, donking the strongest part of your range can make sense. Same with a player who doesn't cbet but will call bets to the river with less than TP. But these are specific cases where donk betting makes sense, but taking a donk bet line in general makes your hand harder to play in most cases such as in your example.