It did make me mad at Castiel, yeah. Because there must have been an easier way to show Dean what was going on, instead of putting him in a situation where he thinks he can change things and then it turns out that he CAN'T. I don't think Castiel quite understands how this works yet. It could very well be that he is used to a non-linear view of time, and when he said "stop it," every time he was talking about Sam and his evil thing, but Dean didn't hear it that way. Whether it was unintentional or not, Castiel was not doing Dean any favors here.