It's not just about the sellI mean GTA, Call of Duty, Skyrim, Red Dead Redemption, and so forth have some of the highest selling games of all time and all are rated M.
I don't think it's much to worry about.
A rated m game can't be advertised for kids. It can't be a "family game" a lot of people who would pitch in on the game (advertising etc) will back out if it's m.