Wow. That's pretty harsh.
I kind of liked the movie.
As with most cinematic offerings, you simply have to go with it and not look with too critical an eye, otherwise you're reduced to nature documentaries and reality TV.
Of course you shoot the horses.
Just like you walk to the back of the saloon and shoot the good guys as they try slip out the back. Or shoot the hero as he broods his way through his second bottle of rotgut whiskey prior to the big showdown.
Or you arrest the guy riding the same horse and wearing the same pants, boots, shirt, hat, and guns as the guy who robbed the stage the night before.
But you don't do that. It isn't good story telling, and it offends our sense of fair play.
In fact, there's only one western I can think of where the bad guy kept kicking the good guys butt, he never got back up after being beaten, he never got any better with a handgun, and the only thing that stopped his antagonist was a well placed shot from someone across the street. And that was 'The man who shot Liberty Valance.' Still has some holes, but a lot closer to a realistic situation than most.