A certain segment of our society has spent a couple of decades trying to convince us that there is nothing worth going to war for.

From a certain standpoint, are they right?

If you did a thought experiment on what the consequences would have been if everybody had simply surrendered to Nazi Germany and Japan without firing a shot, it is difficult to come up with any casualty count from the resulting regimes that would have remotely approached the actual death count from WWII. At least not for many, many years.

Is this valid thinking?

"Conquest" is not identical in meaning with "war," which is why the rape analogy falls flat. As with any other action, motivation has a lot to do with the morality.