I always wave, unless the hand is busy. Always have and always will. Not sure just why actually now that I think on it. The "I got yer back" thing is part of it.
Other than that, riders are a small community. Real riders even smaller. And hell, a little friendly attitude never hurts.
"I wish that an influential person would write a viral piece coming out against waving."
I'm no activist, but I would get on a quick against that one. Some things just need an opposing view. Do you realize that you actually want to start a campaign against being friendly?