I used to listen to a lot of TotalBiscuit (I know) and always felt massively uncomfortable whenever he'd start talking about 40k stuff. He'd go from this nerd games critic to gleefully saying "exterminate the xeno for the emperor" and it never felt humorous, it felt like a weird power fantasy he was indulging in. I guess that's how a lot of nerds end up viewing the Space Marines.
Personally I was always more into the Necrons. They're robots but also skeletons, so it's like the best parts of the two coolest things.