People would rather skip the entire level than trying to beat it alone so is still a bad thing for whoever created the level, I think.I think when you play through a level in multiplayer, your ratings for said level would be separated into a different category reflecting that.
And hey, maybe you could make levels that can only be played in single-player. If people try to play that level in multiplayer, they would find that feature disabled since the designer did not allow it.