Idk, I just find calling yourself "agnostic" to be silly and inherently cowardly. It's like you're afraid of annoying incorrect people by being correct so you just pretend not to be correct instead.
Are you "agnostic" on the topic of unicorns, Bigfoot, the Loch Ness Monster, the flying spaghetti monster, and Russel's Teapot? No? You're comfortable saying those things don't exist? Then the only reason you're not comfortable saying God doesn't exist is because you're concerned about how people who think God does exist will react to that statement. I find that cowardly.
Actually, I think this issue is really interesting. The thing is, throwing the ball underhand is not useful for any other aspect of the game. So if you train free throws underhand, all that training time is being spent solely making you better at free throws. But if you shoot them overhand the same way you shoot from anywhere, then all your free throw practice is also making you better at shooting in general.
I think if basketball players were immortal, they would all eventually shift to underhand free throws, but because they're humans with limited amounts of time to exist, it simply makes more sense to always shoot overhand.