If the only reason to turn them off is so drivers don't pass through ghosted cars, wouldn't it make more sense for drivers to just make sure they don't go through ghosted cars, and if they do, to give the position back? Sure, it might cost them other positions, but realistically, hitting spun out car in real life would have much worse consequences than losing a few positions.
You should be prepared to slow down and go around a car if it has an accident. If you notice it's ghosted and decide to drive right through, you can't really blame the penalty system for losing positions.
If we're just talking about turning penalties off so there won't be any cases of passing through ghosting to look for, that's silly too. If we do that, we'll have to look for cases of corner cutting instead. I would imagine it's easier to look for ghosted cars and see if people go through than to watch the replay for every car and see if they cut any corners.