Is "you lack morality" a viable argument?   stance: no. it's a guilt trick.:
Absolutely not because everyone's sense of morality is different. Thus, for example, if a pro-choicer was engaged in an abortion debate, the pro-lifer could call them moraless all they want but still not change the fact that the pro-choicer has valid points. Indeed, in many cases, morality is extremely subjective and thus saying that someone "lacks morality" is about as valid an argument as "you suck".