Perhaps, and maybe I need to watch the scene again, but it didn't seem to me Milton was under any immediate threat considering the Walker was still mostly restrained. But I do agree there may have been a better way to perform the study without him needing to be in the room but limited resources, I guess.
I still think the Walkers don't strictly have "memories" probably just more autonomic responses to stimuli, whatever that may be. Using tools and such (the Walker with the rock at the door) may be more inherent to "fresh" Walkers whose brain still hasn't largely degraded with the passage of time, maybe the earlier one turns the better intelligence they have (as the brain would be "less degraded" as it reactivated sooner.) But I don't think most of this is all that important to the story they want to tell as since the end of Season 1 it seems not much time at all has spent on trying to explain the Walkers and exactly what's happened over the last year-plus.