Consider for a moment that a user contributes, or can contribute, more than just space. They can contribute processor power as well. Say I was “farming”, contibuting processor power while I was away from my computer and contributing space as well. Granted I might come back at some point but if I put in enough processor time during my afk hours doesn’t that mean I’m entitled to more space measured one presumes in safecoin? Also over time a lot of the files on one’s hard drive won’t be unique to the maidsafe system. They’ll be unique to one’s local system but not the network. Therefore the way to put data on is to submit new content. So in order to fill space on the network you need new content. Offering free space allows people to use the network. Do you want to give up space on your hard drive to store things on dropbox? No, you want to store a copy of your files on dropbox.