He does have a point. It could cause arcing, which will 'cause carbon build up, which occurs anyways, so it's probably not so much ruining your motor as much as wearing it out a little quicker.

But in reality the pulses are so quick that the motor is not completly stopping and starting. So I doubt there really is any difference.

Sure, I have no proof that it doesn't wear out the motor faster, so it is possible. As to how it would cause it to wear faster I have no idea, but I'm no electric motor designer either.

I just don't have it happening to me (yet).