There are several issues with the link you have used as the basis of your question, but ignoring those, I will answer the underlying question.
Karma decides quality of life
The body that a soul takes birth in is primarily determined by its karma, in a way that it can get appropriate reactions and nullify the karma (in minute parts per birth, but that's the goal). Some of these may require being born as a plant, as a microorganism, a small or large animal, a fish, a bird, a human, etc. Within the human form of body, there are further divisions such as the four varnas (brahman, kshatriya etc.), and others such as chandalas who are considered outside the varnashram system.
There are several activities that were considered not acceptable for anyone within the varnashram system, but the chandalas and similar classes could engage in, including consuming the meat of cows, making leather products etc. Their status in the human society is of course much lower than the other 4 varnas. What needs to be understood is that their existence is still essential for those souls to receive certain karmic reactions that they could otherwise not have received. Therefore, despite their deplorable living condition, their presence was not meaningless.
The problem with the question/argument
Further, a similar argument could be made for any of the lower life forms, or for that matter the living entities in hellish planets. While life is very difficult for all of them, it's not unfair, since it is simply a reaping of karma that they sowed themselves. Lord Ram and Lord Krishna do not directly interfere in the cycle of karma, except for those who specifically approach Him/Them. There are many historical instances of those rejected by the society being delivered by Lord Ram or Lord Krishna. The basis of this difference in treatment is Lord Krishna's statement in Bhagavad Gita:
As all surrender unto Me, I reward them accordingly. Everyone follows
My path in all respects, O son of Pṛthā.