There are many ways of cultivating like Qi cultivation, soul cultivation, body cultivation…, etc.
But based on the moral and humane nature, people gave them further classifications like Righteous path, Evil path, and True Devil Path.
These categories are for all the cultivators following any cultivation way whether it is Qi cultivation, body cultivation, or any other way.
The Righteous path mainly refers to the cultivators who cultivate without causing any unnecessary harm to others just to raise their cultivation. Some people on the righteous path see themselves as cultivators with high moral value and principles who needs to be looked upon by others.
The Evil path is the way followed by the cultivators who can go to inhumane heights to raise their cultivation without hesitation, like using the blood, flesh… their whole body of other cultivators, beasts, or even mortals to raise their cultivation base, these type of cultivator have ruthless nature. The cultivator on this path doesn't believe in right or wrong, they only believe in strength.
According to them the word right and wrong are only made to fool weak people while the strong are not bound by this system and can decide on their own definition of right and wrong for people
This path can increase the cultivation base of a cultivator faster compared to the righteous path, the cultivators following it are called Evil Cultivators. They are always detested by the people of the Righteous path and vice-versa if the people of both paths meet each other then there will likely be bloodshed.
The cultivator on this path mostly retains the looks of their base race with slight differences sometimes.
Next comes the True Devil Path, the cultivator following this path can go to any lengths to increase their cultivation base, they won't think before completely destroying the souls of thousands if they can get enough benefits. For the cultivator following this path, they can have the same definition of justice as the people of Righteous path or Evil path but….. no morale, principle, good, bad, blood relation, sworn relation can get in the way of their desire for strength.
The cultivators on this path don't care about their looks or appearance, they can sacrifice their looks or the appearance of their base race to gain strength and longevity resulting in chimera like bodies or monster like appearances.
They are the type who won't try to justify their way but would do whatever they like, and because of the methods used by these cultivators, their cultivation speed is faster than the other two path followers.
For example, there are three people A, B, and C following the righteous, evil, and true devil path respectively, they initially have the same innate talent and resource at their disposal. then the one whose cultivation speed would be highest will be C then B and in the end, will be A, this is of course without any uncertain factor interfering with them.
The reason behind this is that the evil cultivators and true devil cultivators can even use the dead bodies of their enemies as resources to enhance their cultivation base
Furthermore, they would get things like pills and herbs that can help them increase their cultivation base by any mean possible like robbery, murder, slaughter....etc while many normal people in the righteous path could do that too but emotions like guilt, fear..etc would affect them more compared to the other two.
(Note: The cultivation speed of the people following any path can be fast or slower based on their innate talent, pills used, spirit roots, physique, etc… which is somewhat common for other paths too.)
There are also people who don't focus on any of these paths and have their own way of defining their life rules, like what they call justice, right or wrong. Their point of view may be different from others their way might look very similar to one of these three paths but their way doesn't get along with the other people following these three paths.
For example, Rex's way
Rex's belief contradicts others' thoughts, he chose to follow the principle which restricted him from using any methods on anyone besides him. In other people's way if they had such abilities they might not be so friendly to people around them and would have used them to get the maximum benefits. Like if it was righteous path cultivators they would just target evil path cultivators to turn them into slaves and vice-versa to get power, status, and fame.
No one would go through the effort to make Fake Soul Seed and would directly turn the people in Zombie (Of course the resultant would be Lesser Zombie, not Undead Zombie). They won't go through all the effort to consider other's feelings or worry about morals before taking any action to fulfill their wishes and the people with these types of thinking are the ones Rex hates the most.
It doesn't have anything to do with true righteousness or justice defined by others, it's just they are not pleasing to Rex's eyes. For him, they are…..scums, that needed to be eliminated or stay far away from because they might try to use him after knowing his abilities or they might even go as far as to show greed for his abilities and try to find a way to get them or they may also try to harm the family he builds so far.
(Note: Rex's belief are designed with his character it has nothing to do with being correct and being right or wrong in the world)