i think the original point was that git makes random decisions when merging, which forces the git user to look at the result and make sure git's making those random choices to everyone's liking.
the preferred situation would be that a version control system is deterministic and consistent, i.e. that given the same situation it will always do the same thing. if that thing is not what you want, then you will know beforehand, and can fix it. if it is, you don't have to check, you just know it's going to be right.
the drawback of consistency is that it's hard to achieve, and it's harder to understand what happens if you don't follow it with your own eyes hunk by hunk (which you can still do btw). the benefit is that if you're smart enough to use your tools correctly, being consistent they give you a lot more power and efficiency. because you don't have to keep making sure they do the right thing every step of the way.
now what has that to do with social contracts and multiple points of truth? if git were consistent, how would that change the balance of control and authority in a team using it? doesn't consistency, rather than limiting your choices of what hunk goes where, only make it easier for you to implement those choices?
i like git a lot, btw. (-: