Millions of people believing in something does not make it true or correct.
Millions of Muslims and Christians believe that Hindus are worshipping false gods, and they will go to hell if they don't convert to Islam or Christianity. Will you "respect their sentiments" and do as they say?
Any opposition to the project should be only on the basis of ecological and environmental considerations. When religious considerations come into any decision of importance, all logic and rationality go out of the window. Under those circumstances, how can one make an optimal decision?
I agree that historians, scientists and archaeologists should decide if the Setu was indeed built by Ram or not. But supposing their findings say that it is just a natural formation, can we appeal to respect for religious sentiments and disregard science?
Hindus should take the lead in rational religion. I doubt if the composers of the Upanishads would be gravely concerned about ancient formations, man-made or natural. Hindus, as opposed to dogmatic faiths, have a long tradition of questioning and seeking for oneself, and the essence of Hinduism is not belief, but truth. Respecting truth should come naturally to Hindus.