I understand Bhagavad gita says varna is by profession and not by birth. But how should I explain it to a non-hindu or an atheist who is too ignorant to read hindu books and argues that casteism is an inherent part of Hinduism and in order to end it Hinduism must be eradicated.
We can explain in following way:
- Gita/Mahabharata and other such scriptures talk about system of classes/divisions which is called varna-vyavastha (वर्ण व्यवस्था)
- In modern day, people misinterpret it with casteism (जाती वाद)
- There are only 4 divisions: Brahmana, Kshatriya, Vaishya, Shudra; In a row form, they are Intellectuals, Warriors, Businessmen, Servicemen respectively; Division/Class is decided based on person's nature
- There can be several castes throughout the world; Many castes disappeared in past and many will be created in future; Castes are actually decided based on family-trees
Hence this is how classes (वर्ण) and castes (जाती) are different. Refer this post for more detailed explanation.
Since "castes" are temporary, there is no mention of them in shAstra-s, hence "casteism" is not inherent part of Sanatana Dharma.
However, it's naive to assume that the classes are always based on person's profession. Their birth also have an important contribution.
Scenario: If a man of Brahmana nature with caste 'X' marries Brahmana natured woman from any caste, then their child tends to be a Brahmana only. If all in their families strictly follow this tradition of marrying with a person of same intellect, then 'X' caste is as good as Brahmana class.
In modern times, however it's very difficult to judge a person just based on family tree or profession. Many love marriages or random inter-caste marriages spoil the family tree greatly and create people with hybrid intellects.
Refer this post on how the inter-class marriages create sub-classes:
What are the order & duties of the children born from intermixing/hybridisation of 4 classes?
What is the Sanskrit word for caste?
First step stop using the word Caste. Stop using their frame of reference.
Second learn, learn and learn.
Hindu scriptures talk about:
Varna (based on Guna for division of labour) and
Jati (based on bloodlines, which includes many varnas)
The scriptures are specific about their usage. What do they mean by the word caste ?
At the time of independence in 1947 almost 2/3 rd of the Kings belonged to so called "backward" castes.
There was a research paper published by London School of Economics which showed over a period of a few decades how the "social standing" of 2 castes got inverted.
Which "caste" did Valmiki belong to ?
What about other religions, Christianity has separate Churches, burial grounds for "Dalits", other Christians don't marry them. This practice is rampant in Southern India where Christianity has been around for many generations.
Similar behavior exists in Muslim community as well.
Systematic Codification and fossilization of Jatis into castes can be traced back to one Criminal Tribes Act, 1871 where a person was de-facto declared criminal by birth if he/she was born in a particular Jati (tribe or community) and these communities were Ghettoized, and were re-located in ghettos and were not allowed to travel and own property. In this process they became bonded labour.
The effects of this are felt even today.
For example, Stuartpuram is one such Ghetto, till 1970s legally it was not rectified.
Cross posting from a different thread where I explain what is Varna and Jati, Are there finer classifications than the 4-varna/guna classification in scripture?
Varna is most definitely by birth. The gunas that form the basis of it are acquired by past life karma which in turn becomes vasana and samskara.
Profession based varna is not tenable because one can change their profession many times in one life. Varna does not keep on changing during life.
None of this means that varnashrama dharma is a bad thing.