Just an observation...
Disgusting porn - the viewer didn't ask to receive it, so someone sent it - they know what the viewer is looking at;
Pleasing porn - the viewer actively sought it out and can convince themselves that no one else knows what they're looking at.
Basically, it's about our dated attitudes to sex
That said, I agree that indiscriminately distributing porn via email is unacceptable given that many children have irresponsible parents who let them use the Internet without supervision, or who abdicate their responsiblities to third-party software products.