Why Spam is a problem

I'm no fan of spam but we all get snail mail ads don't we? Shouldn't
advertisers of a possibly good product be allowed to e-mail adverstise? If
you could block snail mail ads, and you can, shouldn't the idea of working
on filters and so forth be the way to go? Perhaps it should be the ISP's
responsibility to block spam if you request it. All we need is the
politicians making new laws to stop things!