The truth about spam? (the canned stuff, not email)

Spam is made from pork shoulder meat, right?
What is so bad about spam that people seem to hate? Why does it have such a bad rap? Is it all just their imaginations, rumors, and myths? What is your knowledge about the product? I’m talking about the canned stuff, not email. And what exactly keeps it from spoiling on the shelf, since it seems to need no refrigeration?

Should I really not eat it? I’ve never had it before, but I’m a little nervous to.