Unpopular fact on the present day caste system.
About varnas and jatis.
Looking at the vedic text there seems to very little to no mention of jatis as a system within the varnas. According to ancient Indian literature there is more reference of varnas and hardly no mention of jatis as a system within the varnas.
The origination of jatis is said to be during the Gupta Empire (3rd century C.E to 6th century C.E)
It is to me remembered that only post-Vedic texts have given more emphasis on jatis and the untouchable outcastes while the Vedic text don't mention any such concept.
According to the Dharma shastras as researched and translated by Patrick Olivelle, purity-impurity (i.e. touchable or untouchable of sort ) is only mentioned in the context of individual's moral, ritual and biological pollution(eating certain kinds of food such as meat, going to bathroom)
Looking at post- Vedic shastras too, there seems no instance of pure and impure being used in the reference of a particular group of individuals or a varna or a caste.
Shastras from the 1st millennium mentions about people who do grievous sins and fall out of their varna and are considered impure.
Hence purity and impurity is not to be related with a certain dharma rather an individual. As all varnas could posses impurity and purity on the content of their character, ethical intent, action, innocence or ignorance (acts by children) and so on.
The post-Vedic texts, particularly Manusmriti aka Manava dharmashastra or law of the mans mentions outcastes and suggests that they be outraised (exiled or excluded from a group). This trend is what has stuck on and caused the modern caste system.
There are also mention of the varna system being a interchangeable or shift able system where an individual may shift from their initial varna to another varna or caste on the basis of their morals, ethical purity and so on.
Early Vedic period mentions two varnas dasa and arya. The arya considered themselves as superiors and the rival tribes as dasa. They were also frequent allies but later on seem to be assimilated into the arya society however in a servile position giving rise to them being eventually called dasa aka servant or slave.
The Rigveda society was not distinguished by occupations. No occupation had any stigma behind them and every position was given importance.
Towards the Atharvaveda period the 2 varnas became 4, dasas were renamed as shudras, aryas as vis or Vaishya and the new classes of priests and warriors, i.e. Brahman and Kshatriyas were developed.
The later Vedic periods (100 to 600 BCE)
The artisans are shifted into the Shudras while the brahman and kshatriyas are given special positions.
The Vaishyas are oppressed at will and the Shudra are beaten at will.
It is also to be noted that the aboriginals and the minor tribes of Indian subcontinent were also placed into shudras. While the varnas having more affinity to Europeans were made special.
This seems to be the moment of gradual shift of the varna into the present day caste system.
Reference: Caste system in India
TlDR: The modern caste system is not what the creators intended. The concept of purity impurity is based on morals and ethics. No mention of untouchables is found in the Vedic text but only in post-Vedic texts but in a different concept as someone who has considered a great sin.