It is true that the strong oppress the weak. However, although many people use this to justify themselves oppressing beings weaker than themselves, they are not too enthusiastic when they themselves are oppressed by stronger beings.
For example, one of my friends argues that he is justified in killing animals because they are weaker beings. However, he also complains about the government, banks, or rich people in general oppressing him.
Most people will point to the law of the jungle when it benefits them, but when it doesn't benefit them they will argue against the law of the jungle.
In my opinion, it is best to try to stay away from these people. If they don't care about others, why should you care about them?
The strong will oppress the weak. Some will help the strong while some will help the weak.
Oppression is all around us. We see it not only in domination of one species by another species (e.g. humans dominating cows) but we also see it within species. That is, humans oppress their fellow humans. When a billionaire owns a factory and a wage slave must work in this factory to feed his family and pay the mortgage, this is oppression.
Oppression is everywhere and will likely endure for as long as humans exist. However, this does not mean we should throw our hands in the air and give up. We can all play our role in reducing oppression.
As I said, when there is oppression, there are those who will help the strong and there are those who will help the weak. Usually those who choose to help the strong are doing so for self-interest. For example, if you work for a slave owner and you are paid an income for helping to oppress slaves, you'd likely want to make excuses for doing what you're doing. If you're eating meat and you enjoy it (or you find it convenient), likewise you will tend to make excuses for doing what you're doing.
Reacting to oppression with more oppression
There are those who, when they are angry at being oppressed, react not by attacking their oppressors, but they react by oppressing those weaker than themselves. For example, if a manager at a factory shouts at a worker, the worker may come home feeling angry and depressed, and and he may take his anger out on his child who may, in turn, take out his anger on the family dog.
Then there are groups that have been oppressed. Much is being said in the media today about the so-called "losers of globalization":
In a nutshell, the thesis holds that "globalization" has led to profound economic changes, which have transformed and divided societies. The ones who profit from these changes, mostly better educated and mobile (upper) middle classes that work in the service sector, are the "winners" of globalizations, and support the mainstream parties that have implemented neoliberal policies. The ones who suffer because of these policies, mostly lower educated men in the industrial sector, are the "losers" of globalization and support populist parties.
It is interesting then that these "losers of globalization," rather than channel their anger at their oppressors, are attacking Muslims or migrants or other weak groups.
There is a natural desire for those who are oppressed to seek easily available victims on whom to unload aggression. A junior manager being bullied by senior managers may take his anger out on his workers because he can safely do so. If a working man is being oppressed by his boss, he cannot easily hit back at his boss but he can easily kick those around him who are already downtrodden. A father or mother dissatisfied with life can take their anger out on their children because children are small, weak, vulnerable, and, more importantly, they are easily accessible and available to be oppressed.
This is why it is important to protect yourself from others. Never put yourself in a position where you hand power to someone else to control your life, even if initially they seem nice. Aggression can be triggered easily in a human simply through oppression, and oppression is everywhere in the world.
Protecting the weak is a natural instinct
Many of those who seek to help the oppressed do so not through self-interest. They do so because they care about others.
The instinct to help the weak is natural. It is stronger in some than in others. If we see a puppy being beaten on the streets, we are likely to want to intervene if we can or if we have the courage to do so, but the level of compassion people have for the puppy will vary.
Just as I cannot save all men I cannot save all animals. Oppression is likely to endure for as long as humanity exists. But for me, it is easy to replace animal products with plant-based equivalents and reduce demand for animal products thereby reducing animal suffering. I'm not saying everyone needs to do what I am doing, but this is what I am doing.
Firstly, protect yourself from oppression. Once you are free and shielded from oppression, help those who were once oppressed like you were.