So in other words, if I will have a choice to ride into the wall or through my teammates, I will be forced to hurt my teammates not to kill/hurt my horse?
You can't even imagine how often i'm forced to ride into wall and other things like that, just because teammates don't pay attention/don't care and don't give me space to ride near them.
Then you will cry cav is bumping you all the time even without enemies around. I know many people don't care about teammates already. But I do, and I'm always trying to avoid teammates. With this change, I would have to learn to not care about teammates anymore, which will be just annoying for both. I feel bad by hitting teammate, but I would feel even worse by losing my horse in stupid way. Pretty obvious choice.
This change wouldn't affect that much maneuver horses, like Arabian Warhorse (it can avoid most obvious obstacles pretty easily, thanks to it's maneuver and stopping abilities). Like that horse wasn't the most used already, you want to make it even stronger.
Also, this change will encourage wall camping even more. Like it wasn't hard enough already to kill someone in corner/near wall/on stairs etc. If I make mistake, and stop my horse on the wall near enemy, it's high chance I will lose my horse or I will be killed by ranged (I'm standing target for them, easy shot), so it's already risky thing to try killing enemies near walls. I think it's good enough as it is, since you can sidewalk/jump to side like crazy monkey and avoid charging horse pretty easily (if you see him comming of course). Charging wall on purpose and trying to kill good player standing near it will end horseman's life really quickly.
I don't do that, I don't charge wall straight in, but I sometimes hit the wall trying to avoid teammates or when I misjudge speed/maneuver of horse and hit the wall on light angle (horse then stops immediatelly, no matter how low the angle was). Sometimes horse stops on strange obstacles like little rocks/baskets/other little obstacles just lying on the ground/invisible walls. Most of the time enemy can hit me/my horse few times (1-2-3) before I can ride away, if I get hit from Arbalest in chest or any bow in head I would be dead, isn't that enough punishment?
So maybe this idea has some sense in terms of realism (yeah, hitting the wall would be painful, but I think horse would stop itself before hitting the wall anyway). From gameplay point of view, I don't really see anything good this change will bring.