First of all, no one here has posted anything the slightest bit critical of my decision. Thanks, friends.
But as I've had to explain to my more able friends, my knees were a problem, but they weren't the biggest or worse. My back, and most of all my defective sense of balance, are worse troubles. I've never felt comfortable on a bike. No need to force myself on one. From the reaction of some of my cyclist friends, I'm SUPPOSED to. The fact some people assume I HAVE to ride justifies my decision IMO.
Will I ride again at some point? Who knows? But in the meantime I'm going to enjoy myself and not open my wallet to repair or upgrade gear so I can be uncomfortable and make other people feel good.