So what is the difference is grown men playing with plastic toys in a casual environment versus grown men playing with plastic toys in a competitive environment? How is one aberrant and the other not? If your definition is aberrant behavior is competitive 40K players, then you might be a little naive on the ways of the world. There are much odder and stranger things lurking out there.
I'm not into playing tournaments but there is nothing inherently wrong with competition. We are surrounded by it. Professional sports, the heavy focus on competitive games in the education system, the general race to "get ahead" in our careers.
Heck, GW still pushes competition when it's convenient for them. The Golden Demon painting competition would be a good example. And back in the day, it was GW that created the 40K and fantasy tournament scenes.