Your write-up is quite simplistic and hence is very much open to misinterpretation by non-Indians.
I highly suggest that you consult the works of Patrick Olivelle and Susan Bayly to get at the real History of "Caste" (Varna vs. Jati etc.). That way you can present what is actually stated in the Hindu Scriptures vs. Their misinterpretation and later practice within Indian Society.
Excerpt from https://en.wikipedia.org/wiki/Varna_(Hinduism) :
Recent scholarship suggests that the discussion of varna as well as untouchable outcastes in these texts does not resemble the modern era caste system in India. Patrick Olivelle, a professor of Sanskrit and Indian Religions and credited with modern translations of Vedic literature, Dharma-sutras and Dharma-shastras, states that ancient and medieval Indian texts do not support the ritual pollution, purity-impurity as the basis for varna system. According to Olivelle, purity-impurity is discussed in the Dharma-shastra texts, but only in the context of the individual's moral, ritual and biological pollution (eating certain kinds of food such as meat, urination and defecation). In his review of Dharma-shastras, Olivelle writes, "we see no instance when a term of pure/impure is used with reference to a group of individuals or a varna or caste". The only mention of impurity in the Shastra texts from the 1st millennium is about people who commit grievous sins and thereby fall out of their varna. These, writes Olivelle, are called "fallen people" and impure, declaring that they be ostracised. Olivelle adds that the overwhelming focus in matters relating to purity/impurity in the Dharma-sastra texts concerns "individuals irrespective of their varna affiliation" and all four varnas could attain purity or impurity by the content of their character, ethical intent, actions, innocence or ignorance, stipulations, and ritualistic behaviours.
Olivelle states:
Dumont is correct in his assessment that the ideology of varna is not based on purity. If it were we should expect to find at least some comment on the relative purity and impurity of the different vamas. What is even more important is that the ideology of purity and impurity that emerges from the Dharma literature is concerned with the individual and not with groups, with purification and not with purity, and lends little support to a theory which makes relative purity the foundation of social stratification.