I've never really understood why so many are so vehemently against long putters, belly putters, whatever. I've had many entertaining arguments with Shiv over the years over many different topics, but this time (and it's not the only time!) I think he's dead right: don't scrape, spoon, drag, whatever, just hit it in the hole in your own way.
For every problem that these putters "cure", they create new ones. You can't tell me that your body won't move at all when you have something anchored against it, that's just an added complication, offsetting the advantage of removing the hands. I personally feel like I need the feeling of my hands swinging freely, I know the putter against me would bother me. And you'll never convince me that spending time practicing anchored putting doesn't adversely affect feel for other shots around the green. Much like a golfer has to make adjustments when putting or chipping from off the green, the lack of anchoring presents another complication in that equation.
It's just different, it's not wrong or illegal.
I do kinda wonder if they would have even developed if there weren't the drive for perfectly manicured greens that roll like billiards tables, but that's a thread for another day...