Word "secular" is added into constitution by Mrs. Indira Gandhi due to pressure of communists who were giving support to her government. Many other decisions of that period includes nationalization of the banks on pressure of the communists.
The very aim of injecting word secularism into the constitution was to undermine identity of India and leave it rudderless. Communists often acts as puppet of Chinese that was evident during '62 conflict. Now still they have not given hope of bringing revolution in India as their strategic and tactic supports to Maoists and Naxalities in both Nepal and India. They are really bane of Indian society and severely abuses freedom offered by our democracy.