I suppose everyone gets the stuff advertising viagra in less than discrete terms along with other stuff and stupid stories with no point etc. I was advised never to try to return the mail as it proves you 'exist' as they are fishing for addresses. But why should one have to put up with it and who are the creeps that send it anyway?
it's just the price of the internet... there's a cheap and easy way of sending messages so people use it. (The actual fishing and sending is more likely to be done by robots than by people.) Actually, it's quite possible that ads for Viagra etc come from genuine trading concerns who do their business online and it's over to you whether to respond. But a lot of junk mail contains viruses etc, so you should never open an attachment from someone you don't know.
The thining with Spam emails is it's realatively cheap to send thousands of emails, it may be that only a handfull of people respond but that is enough to justify the costs.
This has never been possibly with standard postal mail as the cost is so prohivative.