Well, if I'd tell my employees to do something stupid, I'd expect them to tell me why it's a stupid idea. But I also wouldn't fire them for talking back to me...
Definitely. And likewise, if my manager told me to do something I thought was stupid, I'd feel totally comfortable telling him (politely of course) why I thought it was a bad idea. Either I know something he doesn't, or he knows something I don't, but either way we want to not do dumb things.