Even as a parent, I will not be that worried when I do find that my son has been looking at porn. Hell I used to sneak a peak at my old mans titty mags when he wasnt hope and it didnt screw me up too bad.
I would just want to talk to him about it and make sure he understands what he is seeing. I also would want to make sure that his friends were not useing my house as their gateway to porn-land. Thats for their parents to worry about not me.
There are much worse things than porn out there.