Metal Gear Solid

Does anyone else think Gray Fox is kind of inconsistent? I just finished MGS1 (again) and he said fighting was the only thing he was ever good at, but at least he "always fought for what he believed in." Did he believe in killing Naomi's parents? What about all the other innocent people he's killed? I'm reading through the stories of MG1 and 2 to see if it would shed some light on this, but nope. It looks like Gray Fox is a legit madman with no morals that just wants to kill Snake. I mean, he even kills the lady he was engaged with and doesn't bat an eye. That really doesn't sound like "fighting for what he believes in," unless he's just admitting he's a shitty person when he said that line.