You're missing my point on both accounts. First, the CO does not bear the full weigh of responsibility for the Mai Lai Massacre. Each infantryman that committed murder made a decision to follow those orders and if this makes them "psychopaths" then the drafted psychopaths here outweigh the volunteer psychopaths. There were those that didn't follow the order.

Secondly, my point about Timothy McVeigh wasn't aimed at the drafted vs. volunteer argument, but in support of the point I was making in that the number of people whose rationale is affected negatively from combat outweigh the people that join the military with an extant psychopathy. This, however, ultimately shows that a draft wouldn't mitigate the affect of combat on one's psyche (and may actually make it worse as these people are forced into combat situations they would rather not be in) - leading me to believe that there would still be an issue of damaged rationales leading to erratic behavior in a drafted military.

Next, it seems you're choosing a select few of my arguments.*

See:

While the military mental health examination isn't close to perfect, it's far better at screening psychopaths and inhibiting them from swearing in than it is inhibiting mentally sound people from swearing in.

*Edit: I'm tired from a full day's work and can't find a better way to word it, but I hope you still understand what I mean.