This is true. I'm trying to remember now why I designed the system to require membership, and having a hard time. I'll look at it again and see about changing it.
Ok, some of it is coming back to me: requiring site registration gave us a way to use the existing user table for donors, and extend on OACS's account management features (/pvt/home, etc) for allowing donors to view their donation history, etc. Otherwise I need to build and manage a seperate Donor table, as well as creating the "donor account" pages. Oh, and, um, providing a password scheme to protect them?
Anyway, if that's what I need to do then that's what I need to do, but that was the reasoning behind it.