Actually, it's NOT a myth. It is just as true today for a certain segment of the archery community as it ever was. Namely selfbow shooters who use their knuckle as an arrow rest. A right hand shooter should shoot left helical in order to keep the leading end of his hen feathers from raking across his knuckle and leaving feather cuts.

Other than that rarified group of true archery connoiseurs, it makes no nevermind which direction your arrows spin. Unless you take the coriolis effect into account.

You know, I've shot right helical and left helical and never saw any difference at all in my points coming loose. Gotta wax those threads to keep 'em from coming loose no matter which way the arrows are spinning. I think THAT right wing/tight points thing is the true myth.