...they were about to get fucked over, pretty badly. Prejudice aside, I think it's fair that they shat bricks and went to fight them.
I've heard people argue (possibly with tongues in cheeks although I wouldn't like to give them the credit) that the Halo series is also not just 'macho wish fulfilment' but also 'anti-multiculturalism', due to how the Covenant (the bad guys) are made up of multiple races and therefore cultures. People seem to forget the flip-side; they're also a genocidal, totalitarian dictatorship who's basis for everything they do comes from religious whims.
I like to think I can spot 'FedEx arrows' most of the time and to be honest nothing about 300 bothered me at all. I can see WHY people might figure it out the way they do but I don't generally agree. Except the 'homo-eroticism', which last time I checked was not a bad thing as such. 21st century and all?