Kadish for 12 months after death of father who violated Shabbos?

Igros Moshe (YD IV #61.6)  Question: Kadish for father who violated Shabbos or was a heretic? Answer Even though it is clearly better to say kadish for 12 months but the Rema ruled that the normal practice is only for 11 nonths so as to not view his father as evil. Obviously he is referring to the typical situation where the father was an observant Jew. However if the son knows his father violated Shabbos even only  for the sake of parnossa the son should say kadish for 12 months. However if he was a heretic, there is no mourning for him, and therefore it makes no sense to obligate him to say kadish for 12 months if he died peacefully in his bed. However if he were killed than kadish is said. However if he wants to say kadish for his father who died peacefully it would seem that it is appropriate and beneficial.  However he has no priority over other mourners.