Too tight or too loose, they're both bad. That's why there is that tang/pawl. Leaving it off, or leaving it loose is just as bad as leaving the cotter pin out of the front wheel bearing nut(s). Either way, you'll lose a wheel eventually.
I understand that, but if you HAD to have one or the other, which is it? Besides, just turning with axle rotation won't be enough to tighten to the point of damage, yet on the left side it could loosen up all the way. So one is definitely worse.