Science distinguishes between animals and plants. Plants have no nerves, are not aware of their environment and cannot flee for their predators.
For a plant to be equipped wih nerves would be useless. If a plant could sense pain or fear, it could not react upon it.
An animal - on the other hand, like human beings - have senses so they can flee for enemies, can search for food and select a sexual partner to breed. An animal acts based on motives, created by agitation of the senses which continuously observe the environment. For infuencing its behaviour, stronger countermotives are to be added.
Philosophy of Law
Schopenhauer: About punishment
Christianity: 10 rules
Buddhism: 5 life rules
Islam: 5 pillars
Tat Tvam Asi
All animals experience pain as an immediate motive: pain has a purpose.
When you burn your hand there is no thinking, your reflex is move back your hand.
When an animal does not submit to the leader of the pack it will be teached a lesson: the pain and the humiliation shall be deeply emprinted in the memory. The prospect of this pain and humiliation shall prove a strong countermotive not to rebel again.
But to inflict pain without purpose is a cruel act. Generally, all living beings shall agree.
Neminem laede, immo omnes, quantum potes, iuva (English: Do not hurt anybody but try as much and as often as you can to help everybody), also see Schopenhauers Ethics.
An also much applied saying is: What you don't want done to yourself, don't do that to another.
Philosophers of all times have struggled to find the foundation on Earth for the righteous behaviour: Ethics.
All religions command their believers to behave according to the Holy Commandments but fail to explain why:
Not all fellow beings are capable of compassion. And even then: Adolf Hitler was able to feel compassion for his dog Blondi.
Leaders who have to take huge decisions, do realize that whatever decision they take, some will benefit and some will be disadvantaged. The righteous decision would be in which most people would benefit and some would be disadvantaged, and the benefits and disadvantages are weighed.
This righteous way of behaviour is defined in the Utilitarianism:
(degree of benefit × number of beneficians) must be larger than (degree disadvantage × number of disadvantaged)
The acceptance of such a decision will be generally beared if the disadvantaged will be properly compensated.
It would be a terrible mistake to assume that because most people agree with all these righteous principles, the desirable behaviour will follow naturally. Most people will agree in principle but they are weak and tend to give in to their sins.
Others do not agree. They will try to take as much as they can, the world is not enough.
And some will not be deterred by anything who we regard as mentally ill.