Point is they climbed it by having a subjugated captive population who were not even allowed to make salt let alone textiles[1]. That population was forced to plant cash crops (primarily cotton) that could then be exported to Britain at fixed prices and sent back as textiles.
There is about 70 years from the start of company rule to the 1830's. If you're not allowed to manufacture textiles in that time period, what exactly do you think would happen? You'd maintain a comparative advantage?
On opium: In India, its cultivation, as well as the manufacture and traffic to China, were subject to the British East India Company (BEIC), as a strict monopoly of the British government.[7]
Opium, like most industries, only benefited the British. So it would be more accurate for you to say the British used the Indians to start exporting opium.
So lets recap. People that mostly export textiles suddenly finds themselves 1) unable to make their own textiles, 2) forced to plant cotton and other crops for sole benefit of the British. So you have a whole civilization barred from selling finished goods. Gee wonder what happens to them.
[1]
Taxation of salt has occurred in India since the earliest times. However, this tax was greatly increased when the British East India Company began to establish its rule over provinces in India. In 1835, special taxes were imposed on Indian salt to facilitate its import. This paid huge dividends for the traders of the British East India Company. When the Crown took over the administration of India from the Company in 1858, the taxes were not replaced.
The stringent salt taxes imposed by the British were vehemently condemned by the Indian public. In 1885, at the first session of the Indian National Congress in Bombay, a prominent Congress Leader S.A.Swaminatha Iyer raised the issue of the salt tax.[1] There were further protests throughout the late 19th and early 20th centuries culminating in Mahatma Gandhi's Salt Satyagraha in 1930. This sathyagraha was followed by other sathyagrahas in other parts of the country.
After the arrest of Gandhi, Sarojini Naidu lead the sathyagrahis to Dharasana Salt works in Gujarat and was arrested by the police. C. Rajagopalachari broke the Salt Laws at Vedaranyam, in Madras Province in the same year. Thousands courted arrest and were imprisoned in large numbers. The administration eventually relented and invited Mahatma Gandhi to England to attend the Second Round Table Conference. Gandhi's Dandi March got wide news coverage and proved to be a turning point in the history of India's independence movement.
The salt tax, however, continued to remain in effect and was repealed only when Jawaharlal Nehru became the Prime Minister of the Interim Government in 1946.