Well, I look at this way: it's the difference between business and pleasure.
When I play computer wargames about the Eastern Front, I am playing for pleasure. I always play the German side because it's always a pleasure to "kill" commies.
When I play Western Front games, I always play the Brits or the Americans because then it's a pleasure to get down to the business of "killing" Nazis.
That's the old joke about who a Pole shoots first. Of course, he shoots the German, before the Russian, business before pleasure.
"We in the killin' Nazi business. And cousin, business is a-boomin'."