The first sentence of the preamble:
WE, THE PEOPLE OF INDIA, having solemnly resolved to constitute India into a SOVEREIGN, SOCIALIST, SECULAR ,DEMOCRATIC REPUBLIC and to secure to all its citizens:
It was part of the 42nd amendment to the Constitution of the Republic of India. It was changed from a "sovereign democratic republic" to a "sovereign, socialist secular democratic republic". Majority believed (and many still do) that socialist organization of a society is better than a capitalistic organization. Few were opposed and argued that it was a superfluous change and socialist principles were already embedded in the constitution. Few were opposed to it because they did not wish to tie the people down to live in a particular way of life- even if in principal.
It, more or less, remains a superfluous issue these days (and speaking from personal experience, most Indians do not care). Few have challenged it in court. In response to a petition change it, a head of a three judge panel mentioned, "Why do you take socialism in a narrow sense defined by communists? In broader sense, it means welfare measures for the citizens. It is a facet of democracy. It hasn't got any definite meaning. It gets different meanings in different times."
The petition was withdrawn after the supreme court declared the issue "highly academic".