As others have stated it hurts them more in some ways as you know the customer was willing to actually spend money on a purchase.
The plus point is that the second hand market is often catered for by people trading in newer games early to get brand new titles for a fraction of the cost they couldn't afford otherwise. There is some swings and roundabouts and its not clear cut.
I never trade my games or buy preowned so it doesn't matter to me but I don't think it's right for any company to have a say in what we do with a product we have bought. I paid for something and should be allowed to resell it if I choose imo, I don't see why a company should have any less rights than me.