When you are flapping hard enough that you are levitating above the saddle, it is slamming the horse in the back when you come down, which will throw them off balance and in the end, slow them down, not speed them up. Not to mention, what about when you are legs straight out, butt half a foot off the saddle and the horse decides to spook, or any other unanticipated movement? Not a very secure seat when you aren't even touching the saddle, and you WILL take a dive. Correlation between rubber banding feet into stirrups and that crazy flapping? Well, yeah, because flapping that hard and keeping your stirrups is a nearly impossible feat. So basically, I'm saying kicking yes, a little flapping in a controlled way, okay maybe. But that god-awful plane taking off, little kid in a bouncy house flapping? No way.
"Keep a leg on each side and your mind in the middle"