Either public support for actions which are gravely sinful satisfy the conditions of 915 or they don’t. Support for abortion does if anything could be considered to meet those criteria.
But [homosexuality] is relevant to the validity of your argument as a counterexample.
Homosexual actions, like contraception, are grave sins, but that alone does not mean they should be classified as crimes any more than one would suggest criminalizing absence from Sunday mass. This is not a new concept.
Now human law is framed for a number of human beings, the majority of whom are not perfect in virtue. Wherefore human laws do not forbid all vices, from which the virtuous abstain, but only the more grievous vices, from which it is possible for the majority to abstain; and chiefly those that are to the hurt of others, without the prohibition of which human society could not be maintained: thus human law prohibits murder, theft and such like. (Aquinas ST II-II 11, 10, 1)
Those individuals who publicly manifest a homosexual lifestyle meet the criteria of 915. Politicians who promote gay “marriage” meet it. A politician who does not advocate criminalizing homosexual behavior does not. Is this arbitrary? To a degree perhaps, but, whatever else may be true, if supporting the destruction of the innocent does not trigger 915 then the law is without any meaning whatsoever.