In single player, you're more than welcome to carry as much as you want or are realisticly able to eg: Resident Evil 4, Fallout 3. However, if you want to take your massive inventory into multiplayer, that's where the BS meter kicks in. If you've ever played Modern Warfare 2, you should know how many people abuse running around and insta-killing with a knife, or carrying a sniper/shotgun setup and destroying people at ranges meant for rifles. The guns aren't the issue, it's the games and the players. Lastly, in games that favor a sort of fictional realism (damn near all) it only makes sense that you can only keep what you carry. If you truly want variety, play some Gears of War.