Animals: why did the Buddha remain silent? I know there have been discussions about vegetarianism, but my question is not exactly that.

I know that: 


The Buddha allowed eating meat for monks, if it is clear that the animal was not killed on purpose (Majjhima Nikaya 55.5), especially to provide the meal. The main premise behind the three-fold rule is to graciously accept what one receives in your bowl when going for alms round. This rule was meant and spoken to monks and nuns, not to lay people. “Beggars can’t be choosers” in modern terms. The Buddha's diet was more likely a vegetarian diet who ate meat "out of pity" on rare occasions.
On various occasions, the Buddha denounced the professions of fisherman and fish merchant as well as butcher. These professions are not part of a just livelihood (fifth of the eight stages of the Eightfold Path), nor is the trade in arms, intoxicants (alcohol) and the trafficking of living beings, human or animal. The ahimsa therefore covers for the laics the idea of not killing animals as well.
The Buddha banned the religious sacrifice of animals.


Knowing this, I don't understand why he didn't ban meat from the laics, or at least recommend a reduction in consumption?

We can clearly see that the Buddha considers meat consumption to be at least an indirect violation of the first precept of not killing, since he forbids monks to eat meat killed for them. Why does he allow meat that has not been directly killed for the monk? I have the impression that the Buddha considers that if the relationship of evil is not directly causal then it is less serious (that is why he allows the monk to eat meat that has not been directly killed for him). This can be understood: kamma is the intention and the one who eats meat doesn't intend to hurt an animal even if that's what he causes more or less directly by supporting the butcher's market.  But then, why not at least say to limit your meat intake?

When we see the horrors of the meat and dairy industry, I don't understand why the Buddha was silent on this subject. Even more if we consider that he was omniscient, so he saw all the suffering that this industry has inflicted, is inflicting, and will inflict in the future.

I understand all the less this silence precisely because, contrary to the Abrahamic religions, there is a form of equality between man and animal in Buddhism in the sense that each man can be reborn as an animal within samsara, and that each animal is surely a human being in the making. Animals are beings in their own right, not resources that man can dispose of as he pleases (Genesis 9:2-3).

I understand the logical reasoning that the Buddha must have had:


kamma is intention.
the one who eats meat has no intention of hurting a sentient being.
eating meat is still indirectly causing the death of the animal, so he forbids consumption in the first degree (if the animal was killed directly for us).


I understand that every action creates suffering, that you have to put an arbitrary limit somewhere so that you don't end up wondering how not to hurt the bacteria? But even if we eat meat that hasn't been killed directly for us, we are supporting a gigantic industry of suffering by doing so; in his compassion, wisdom, and possibly omniscience, I really don't understand his silence, he could have at least asked us to reduce our consumption, I don't know. I find it a bit easy to clear oneself because the animal was not slaughtered for us personally. 

So:

Is the ethics of the dhamma incomplete?
This is mere speculations from me, but turning down meat was probably not a viable option during buddhas lifetime, for the sake of survival. A layperson would likely run the risk of starvation without meat, and making vegetarianism a decree could possibly put a lot of peoples health at jeopardy. 

Again, i am guessing now, but my point is that we can probably only understand a set of beliefs by understanding the context of that time. It could explain the "why" of buddhist ethics. (We could for instance compare this to the muslim decree on abstaining from eating pork, which at least partially is assumed to be for health reasons to my understanding).

You also seem to ask what ethics regarding vegetarianism should be in order to be consistent, which is a bit different than the question why.

Your argument regarding today's meat industry seems anachronistic, since the premises of meat production in those times was presumably a lot different than the large scale meat industrialization of our times.

In summary, the choice of eating meat is likely more feasible today, and therefore the ethical aspects of that choice becomes more salient, compared to buddhas time. Back then, it's possible that the ethical conundrum could be sufficiently solved by deriving karma from our intentions. 

Applying this ethic in todays world, with the meat industry that goes with it may make a much stronger and convincing case for vegetarianism, compared to buddhas time.