We are living in the age of mass theft, or at least that's one way to look at it. The epidemic of software piracy and music and movie sharing is almost impossible to separate from the influx of computer use and especially fast Internet access into our homes. The two occurred so simultaneously that it seems amazing in retrospect that no-one realized what was going to happen.
Human beings are social creatures, and we do like to share what we enjoy. Of course, we are accustomed to hoarding things that are finite and consumable, like food or money, but files? Software? They don't run out or get used up, so human nature dictates that we share them.
Notions of value get tossed out the window when the product is essentially infinite. Unfortunately, the same values and methods of selling are used for digital products as for regular ones, and of course copyright and intellectual property rights still apply.