My advice to the Cubs is stop complaining, put on your big boy pants, and if it really bothers you, throw at their guys. This is how it has always been handled in the past. Today, with the over abundance of participation trophy babies playing the game, anything not grooved down the middle is considered bad sportsmanship.
I for one applaud the Pirates pitchers. They have gotten into the heads of other teams and that gives them an advantage. I'm not saying they should hit a guy in the head but nothing wrong with sending a message.
Throwing at anyone's head is wrong any time. You want to send a message knock them off the plate chest down. Throwing near the head has no place in this game.