Tamil is an ancient language, part of the Dravidian language family. It is one of the oldest surviving languages in the world with both classical legacy and contemporary relevance. Apart from other prominent Dravidian languages in South India, languages like Brahui used in Central Balochistan and Kurukh, spoken in tribal belts of Odisha and its adjacent states, are also Dravidian languages but listed as endangered by UNESCO.
The Tamil language that is in usage today is much different from the Tamil language that was in use during the 3rd century BC. The language has gone through historic phases of evolution, over a span of several centuries. During the Sangam eras, enormous efforts were taken to consolidate changes and additions made to the language. Tamil has seen transformation even post Sangam eras, being influenced by the linguistic and literary efforts undertaken by scholars, and even by colloquial use of the language, which kept changing with times.
For native speakers of languages that belong to other language families like Indo-Aryan, Sino-Tibetan, Austroasiatic, etc., learning Tamil may offer a unique linguistic experience, due to the distinctness of Tamil. Now the same can be said to the native speakers of Tamil as well. If we learn a new language, which is part of other language families, the joy of learning will be unique, because of their distinctness from Tamil.
In today's scenario, learning an additional language can only be seen as an advantage, because we interact and transact with people of almost every country. Those who have a need to interact with people outside their region will be able to say how vital it is to know more languages. In a number of countries, English is in trade usage, as their lingua franca (bridge language). If a person knows English, communicating with people of these countries will become easier. But there are also countries, where knowing English alone will not help. One may need the local language in countries like Russia and China.
People from Tamil Nadu are living in cities all around the world, for business, work, and study. How do they communicate with the local community there? They must be communicating either in English or through the local language. They may not be able to say, "Look, I will only talk in Tamil." So for all practical reasons, they accept English as a common tool to communicate or learn the local language to communicate.
In schools in Tamil Nadu, English is taught as a language of communication, also as a medium of instruction to teach subjects like Science, Maths, History, etc. Often there are two choices. One can either learn the subjects in Tamil, or in English. But students in increasing numbers are choosing English as their medium to learn subjects because it widens their scope for further learning and employability.
On the other hand, learning the subjects in Tamil, as on today, can limit employment opportunities to just institutions within the state, as even private corporates in the state may prefer to hire only a candidate who knows these subjects in English. Only in rare few cases, where parents have a special leaning towards getting their children taught in 'Tamil medium', the choice is made willfully. In all other cases, socio-economic reasons compel them to choose Tamil medium. There are parents who cannot afford to send their children to Private English medium schools. There are some parents who think it's enough if their children learn in Tamil medium, even if the Government run School has both mediums as options. In some cases, people may be living in remote areas with no accessibility to English medium schools.
Incidentally, even people who fanatically preach Tamil, with warcry on every other language, send their children only to English medium schools. They also own and run schools and colleges with only English as their medium of instruction. Whereas, people of the state from the lower economic background, in both urban and rural areas, feel compelled to send their children to Tamil medium schools, due to socio-economic reasons. But this trend seems to be changing. They now think that unless their children get educated through English medium, they will not be able to compete with other students for higher studies or employment. For them, education of their kids remains their only hope for socio-economic upliftment.
Today, English is fast replacing Tamil as a medium of learning, in a state where Hindi was once propagated as a threat to Tamil.