Anyway, it's freakin obvious how much easier it is to pull a trigger with only a little hesitation than to get a brick out and beat somebody to death. I don't understand how you don't see that. It's like you've already made your decision and no matter what anyone says, you're 100% confident you can explain it away before you even see it.
It's obvious enough that killing someone with a firearm is easier than doing likewise with a brick. For a civilized, i.e. domesticated, human, acting upon the urge to kill at all is harder than either; a large part of what we call "civilization" consists in overcoming our murderous heritage. (Or did you think we humans have ended up our entire planet's uncontested apex predator, so much so that many of us never even have to hunt, because we're just so nice?)
And have you considered the possibility that, once you've clobbered somebody in the head with a brick the first time, your perspective on the matter might change? God forfend I should ever find myself in such a position! But I think it reasonable to imagine that, once there, it might seem at least as sensible to keep going as to stop. "Escalation of commitment," I think it's called.