I liked this mission a lot, and liked the follow-up even more.
I found it to be very realistic.
As you say, Bertram has the mind of a child.
And like a child, he is prone to tantrums. Sometimes violent ones.
But unlike a child, Bertram cannot be easily subdued if he presents a danger to himself or to others.
Sometimes violence is the answer. Self-defense, or defense of others, is the most valid defense of violence there is, and it applies just as much when the perpetrator is mentally disabled as it does when they aren’t.
Executing a mentally disabled person for their crimes is of course wrong. But if a mentally disabled person pulls a gun on someone, a cop is entirely justified in shooting them — even killing them — to protect the life of the hostage.
Even so, you do feel guilty about beating up Bertram, even if it was the right thing to do. Because he is like a child.
Of course the scene could have been written differently, but I think it accomplishes what it sets out to do. A huge part of RDR2’s story is about making the player second-guess the violence that they partake in. The Edith Downes storyline is a prime example of that.
And the Bertram storyline accomplishes the same thing, at least it did for me. The violence against Bertram is completely justified. It was morally the right decision. But it still leaves you second-guessing yourself, which is the game’s larger goal.