Geocaching is not free, no matter what anyone tells you. There are costs, like GPS units, internet connectivity and gas for your car (not to mention Band-Aids, beef jerky, and bug dope) that are unavoidable. There are other costs, like premium membership to geocache listing sites along with various shareware programs that can make geocaching easier and more efficient that can be avoided. I've long been interested in why people do or do not pay the avoidable costs, and recently asked a group of geocachers just that question.
The answers I got ranged from the pragmatic to the philosophical. Some people paid for premium membership of various geocache listing sites for the perks (better access or PQs), while others paid seemingly just as a "Thank You" for the fun and exercise geocaching provides. With ancillary software like GSAK and CacheMate, people generally pay to support the software developers and insure future upgrades. Many people who pay for the above attributed their contributions to geocaching related services to a mix of factors.
People who choose not to pay generally fall into two camps: the "I don't pay because it is free" group and the "I can't pay because I don't have any money" group. The free memberships and shareware don't cost anything to try out and use (in some cases indefinitely) for a reason; non-payers aren't stealing anything from the listing sites or from the shareware producers. I hope that the sites and the software always have enough paying customers to make it possible for people without the resources to still enjoy geocaching.
As long as your reasons are thought out, it's my feeling that there's no wrong answer to the question of paying for geocaching services. "Pay-by-choice" is a economic model that seems to work in the geocaching world. Geocaching.com and numerous other geocache listing sites (like Navicache.com and Terracaching.com) are thriving, GSAK and CacheMate keep on coming out with newer and better versions of their programs. By the same token, the sites and programs that the geocaching community doesn't like will eventually disappear due to lack of support. I believe that in the long run, this model will strengthen geocaching through an economic form of Darwin's "survival of the fittest."