http://www.nfl.com/videos?videoId=09000d5d80e86d72
Try again. You can't tell me Dansby couldn't stop himself. Fast forward to the 4 minute mark. Not only did he not even try to stop, but he continued to run through the entire motion. There's no possible way that this would not have been called.
It's not a bad call if it fits the textbook definition of the rule. Whether or not you think it's a severe call is just about as irrelevant as anything could possibly be. I watched this play again on this video (it's right before the roughing the holder call), and it does seem that there should have been offsetting penalties on this play, as Roethlisberger did intentionally ground (I missed this on live tv and concede the point). But to argue that that is not a roughing the passer call is ridiculous. He not only blindsided him, but he was unimpeded on his route to the passer. He may or may not have been able to completely avoid contact, but the hit that he put on him was excessive given the length of time from the time the ball was released and the time he made contact. Again, you can't call it a bad call if it meets the criteria for the call, whether or not it sometimes isn't called.