I can completely understand why you're upset about this.
I think it's one of those times where if nothing goes awry it's easy to say "no harm". But if something had gone wrong, it would be too late to question whether that was a good decision or not.
I agree with A-Squared, if DS was asleep, the need for milk was no longer urgent and he could have taken DS with him when he woke up.
At the same time, I don't want to crucify thre guy completely. This gig is full of "this or that" questions and I don't know that I always get it right either.