I think stopping a good number of amateurs would be better than the hassle that legitimate customers have to deal with. I think the only time DRM is effective is when there is an online component to a game. Single player DRM typically results in annoyance. This article provides a good example of someone who couldn't tell it was the pirated copy delivering that message. If the stolen versions of a game had a defect that was built in well enough (Serious Sam 3) it could dupe thieves for a while.