I've played through System Shock 2, Duke 3D, Doom, Quake 2 + 3, CS 1.6 + Source, Stalker Shadow of Chernobyl, Deus Ex + Human Revolution, Vampire the Masquerade Bloodlines, Fallout New Vegas, and a bunch of obscure Half-Life and Half-Life 2 mods so I've never felt ashamed about playing and enjoying Call of Duty, because I know what other shooters offer.
But even if you've never played any of those, you still shouldn't feel shame. Playing those little girl JRPGs do not make you a pedophile who's obsessed with Japan. Playing Halo does not mean you have your television consistently set on ESPN with a fridge full of beer, a pickup truck in the backyard, a cabinet full of guns, and a low IQ. Playing Nintendo games do not make you childish.