A game designer must always assume that players are, to some degree, evil. If you're going to meaningfully analyze the integrity of a system, you have to operate from the position that everyone, hosts and otherwise, are evil, and nothing you receive from the client can be accepted without validation.
A game designer thinking this way is prudent. I agree. But to have the community think this way, poisons the well. Everyone fearing who they are playing does not help foster a friendly but competitive atmosphere.