I completely agree that turning anything into a no-no tends to make it into a big deal, however I agree with your grandfather as well. He does/did have a very good basis for his position.
Matthew 15:18 "But what comes out of the mouth proceeds from the heart, and this defiles a person."
"I'm far more concerned with..." and "It's only music..." and "What's the harm in watching..." are all phrases that I have recently been covering in my Sunday school and discipleship studies recently. As Christ followers, the things you list, nudity, violence, mindless "culture", should concern us greatly, but so should the lesser things as well.
Matthew 5:19 "Therefore whoever relaxes one of the least of these commandments and teaches others to do the same will be called least in the kingdom of heaven, but whoever does them and teaches them will be called great in the kingdom of heaven."
Philippians 4:8 "Finally, brothers, whatever is true, whatever is honorable, whatever is just, whatever is pure, whatever is lovely, whatever is commendable, if there is any excellence, if there is anything worthy of praise, think about these things."
I am certain my geek card will be revoked for quoting scripture on /. Oh well. It's worth loosing if so.