Disclaimer: I am speaking in general, and not about any of the specifics of Chris Kyle's sniping, which I really don't know the details of.
The "snipers are cowards" bit doesn't make any sense to me anyway. It's cowardly, why? Cause you're far away and therefore the guy you're shooting at can't shoot back at you? This isn't Call of Duty. They put guys in harms way when the operation requires it and they put other guys in other places to facilitate the mission. You may need a guy at a distance with the proper vantage point to take out people who would kill your guys on the ground if they tried to move in without that support. Is it also coward to wear body armor? Is it cowardly to take cover when you're in a fire fight? Why hide behind an object like a little kitty. Be a real solider and just charge your enemy full speed while unloading your clip and whoever wins wins.