Nothing wrong with it.
It assumes the average player is a freakin' idiot. That's what's wrong with it.
Not the avarage player. The inexperienced player. That's where that line is aimed at. And it actually helps, I've seen it with beginning players. Once the board gets too clogged up, they don't want tio attack anymore, even if their crusher wouldn't get killed, in fear of a counter attack.