Is indirect causation relevant in animal suffering?
From a quick search it seems there is a dispute about this among later authorities. In my opinion, by logic it is like all other prohibitions, and there is no indirect causation here. True, in the Talmud animal suffering is mentioned even in a case where it is not done directly, but there it is not stated as a prohibition, rather as a principle that can override prohibitions, and that is different (since apparently any permission for some hidden need would be learned from there, because why should a commandment be superior to some other need). And in my opinion one also cannot learn it from unloading, because that is only according to the view that animal suffering is Torah-level, and because the requirement there also goes beyond the ordinary requirement (after all, it is obvious that there is no prohibition of animal suffering every time one sees an animal suffering and does not help it, so the principle may perhaps be learned from unloading, but not the full application).

Even if there is indirect causation, you can always sell the device to a non-Jew…
And this reminds me again of the medical student and the abortion knife.

Itai,
There are two questions here, a halakhic one and a moral one. My discussion is about the halakhic question. I think that goes without saying.
By the way, the “novelty” that there is also morality is not the message of the story about the student.

The main “novelty” I see in the story is that people focus on Jewish law and forget morality (which I do not see as separate from Jewish law; rather, Jewish law comes—in many commandments—to express morality, and even if one can game the law so that formally no prohibition is violated, the moral issue still remains. The secular people there are only a parable, in my view, for missing the moral point and focusing on the legal one.

I would say the opposite. Precisely because Jewish law does not overlap with morality (see Column 15), the moral consideration remains in force even if the halakhic consideration permits it.
The prohibition is to set traps for pigeons and leave them there. That is not indirect causation, but rather like confining someone, or at least like tying someone up in a place where the sun will eventually come there (see Maimonides, Laws of Murder 3:9-10, where that is considered murder even if exempt from the death penalty).
The question about the prohibition on someone who does not release them is interesting. Apparently there is no obligation of “do not stand idly by your neighbor’s blood” regarding pigeons, but unloading and loading are such cases. And regarding whether animal suffering is Torah-level or rabbinic, the halakhic decisors disagreed, and according to most of them it is Torah-level. True, in Or Sameach on Maimonides (Murder 13:9) he distinguished, according to Maimonides, between animal suffering itself and the obligation to help in order to prevent suffering, but it seems to me that according to most decisors who derive the Torah-level status of animal suffering from unloading, there is no such distinction.
But as stated, the halakhic hairsplitting is not really important here.

I know Column 15, and that is exactly what I wrote—that I do see Jewish law as expressing morality (it seems ridiculous to me to say that animal suffering is a law that does not come to express every person’s natural moral feeling, but comes to forbid animal suffering for some other reason; and so too with the rest of the laws that overlap with morality. “You shall not murder” has its legal parameters, even though it is obvious that the prohibition is not detached from the basic human conception that forbids murder).
Rather, Jewish law has its limitations; morality is the lights and Jewish law is the vessels, and vessels naturally have limitations, because Jewish law comes to establish an absolute boundary in these matters, and therefore it has its own definitions. It may be that someone who transgresses has not violated Jewish law, but the morality that Jewish law expresses still must be upheld.

The halakhic hairsplitting is important from the standpoint of Jewish law.
It is not similar to tying someone up, because there I directly tie the person, whereas here I directly only place a trap. It seems to me that the later authorities say that the prohibited labor of trapping is indirect causation (like cooking), but here the trapping itself is only one stage, after which there is a case of “the sun will eventually come.”
Also, there is no certainty here that “a pigeon will eventually come,” like “the sun will eventually come.”

And what I wrote regarding unloading is that, since it is obvious that there is no prohibition against standing by while an animal suffers, the derivation from unloading is only of the principle of animal suffering, not of the application.

Is this parody responsa?! There is no moral or halakhic problem here any more than with a mosquito killer. Is the next step to forbid boiling water so as not to kill bacteria?!

Indeed. If it weren’t parody, I would delete the nonsense you wrote.