How could 17-people actually reason that it is "moral" to rub one off? It does not harm anyone and is certainly not a sin, but if an Eight grade male thinks he will be canonized for jacking off then he is certainly off base.
If one partner is in the mood much more so than another I would say that masturbation is moral, whether done solo or by ones partner, because it helps avoid getting into a situation where one partner is not getting their needs met (and thus may feel tempted to behave unfaithfully - that is, if he or she is in an exclusive relationship), and the other may feel pressured to have intercourse or go along with other sexual acts when she or he does not really want to do so.