Of course. I meant to ask about the issue more generally through this.
For example, should the father encourage him to get married, or on the contrary even try to prevent him, from a halakhic standpoint?
In other words, the question is whether the marriage itself is a commandment and a positive thing even if the problematic halakhic consequences it will bring are clear, or not.

This is a broader question from several angles. For example: from a Torah perspective, is life in itself, even without observance of commandments, positive and itself the fulfillment of a commandment (such as “guard yourselves carefully” and the prohibition against suicide, etc.), except that it contains deficiencies in the observance of particular commandments? Or halakhically, if a person does not observe commandments and commits transgressions punishable by karet, is it in principle preferable that he not live, and if there were a religious court, etc., that would already happen—but substantively that is the situation?
I would be very glad for an answer with halakhic sources, of course, and thank you for all your work.

Even if there were a religious court, etc., that still would not already happen. It was rare for the Sanhedrin to execute anyone, and not for things like that. And you know what they say about it in such a case. Go and learn.

The question whether life is a means for commandments or not is discussed in Column 421. There I explained that in my opinion life is a value in itself.
I think one should distinguish here between a gay son, whose marriage is inherently a prohibition, and in that case I would not push him to get married (though I also would not oppose it, because we are speaking of complete coercion), and the marriage of a secular child, where there are not necessarily prohibitions involved. He will decide whether to conduct it according to Jewish law or not. It is like the obligation to save the life of a secular person, even if the rationale for overriding the Sabbath is, “Desecrate one Sabbath for him so that he may keep many Sabbaths,” while in fact he will not keep them. Even there, the obligation is to save his life and enable him to keep many Sabbaths. What he does with that is his decision. The same applies here.
Moreover, marriage has a role in a person’s life regardless of whether he conducts it according to Jewish law or not. A couple-unit is socially important and important for the spouses themselves as well.
I do not produce sources for questions that have no clear sources, and certainly not binding sources. In such situations everyone does with the sources whatever his heart desires. I wrote my opinion, so now at least you have one source.

Here is one line of thought that occurs to me:

The father’s attitude depends on the alternative. If the son will increase the number of transgressions in the world because of his marriage, then this is a saddening step. If in any case he is already committing those same transgressions, then it is a happy step, because if he will not have the World to Come, at least he should have this world…

And what about “when the wicked perish there is song”? And “I hate them with utmost hatred”?

I am assuming that he is not a wicked person of the kind one is commanded to hate and to rejoice at his death, because of the spirit of heresy in the world and the religious situation among the Jewish people, etc. (as explained by Nachmanides, the Mahari"l, and the Chazon Ish). And even so, it may be that he has lost his spiritual world, at least a central part of it.

Thank you, Rabbi, for the answer.
The source you brought from “Desecrate one Sabbath for him” is certainly valid with respect to the “reasonable person,” who would not dare say that this law does not apply to a secular person (while regarding the wedding question he would hesitate).
Although everyone will still interpret every source according to what he thinks, I would still appreciate it if you could nevertheless throw out a few sources here in both directions. Also regarding the topic of whether, in weighing the sides for the fulfillment or non-fulfillment of a present commandment, one takes into account the likely future reality.