There's a very clear logical connection. If Hitler had been concerned to maintain peace with France or the Netherlands, but somehow against his intentions he had become involved in a "wrong war" with them, when he really intended only to fight the commies - that is a preposterous reading of the situation by the way - then after defeating these unintended opponents, would he have treated them with such murderous rapacity?
I don't think I ever suggested that Hitler had not intended to fight a war with the western european powers, so if that is what you were arguing against then I can only agree with you.
We seem to be disagreeing about the possibility of a peace agreement with Britain. That possibility, in my mind, would be based upon the fact that Germany had three possible weapons to use against Britain: invasion, blockade, and strategic bombing. In hindsight we can see that they wouldn't win the war with any of these, though at the time it wasn't so obvious. Still winning a war with Britain
was obviously going to be more difficult, time consuming, and expensive than had been the war with France, and, particularly blockade did risk bringing the Americans into the conflict. Had Britain been willing to sue for peace, there are good reasons for Hitler to have considered it, as while it may have been an objective it certainly wasn't his only objective.
I would suggest that war with both Britain and France was pursued in order to avoid their interference with his other objectives. His initial victories may have been enough to win concessions in that regard, perhaps enough that he would have been happy with a peace.
I don't know, but it doesn't seem impossible to me.