Just makes it more fun
Plus, guns back then had poor accuracy. So I'm sure the AI's aiming will be terrible
You've not played GTA games much, have you? lol stuffty accuracy, yes but it doesn't matter if a whole posse is after you on horseback pelting away. It only takes one lucky shot and poof. I know that the AI in GTA IV always had supernatural accuracy, more so in groups. Out on the plains, there's nothing to hide behind.
its not like you wont be able to shoot them first
In which your passengers are sent careening off a cliff because no one is steering and the horses break loose on a sharp turn. Game over man, Game over. :(
Also, I can't wait for the Native American factions to go ballistic over the fact that you'd probably be able to slaughter entire camps in free roam or something of that degrading nature.