Have you seen what Destiny looks like? The art style is more akin to a bright, colorful, [i]hopeful [/i]fairy tale. We're not dealing with dark gritty bloody Gears of War. Good stories are fueled by many different things, but blood and guts is not one of them.
Also, people can get shot and die in any rating. Look at movies like Bambi and The Lion King, made for kids. Halo's level of violence was perfect for me. I don't need my characters screaming the F word to get the point across, because it can be articulated through other things.