The soviets dispatched two groups of ships armed with nuclear weapons into the bay of Bengal 5 days before the Enterprise arrived which begs the question, who was threatening who here? Yes, the Enterprise group had nukes. So did the Russian ships already there. the Enterprise group was there to facillitate evacuating Pakistani forces. It was only when they realized that soviet nuclear subs were tailing them that they withdrew. Again, who was threatening who here? keep in mind, all of this was to prevent the spread of Soviet Communism which was pretty well recognized as evil by everyone back then. everyone except India I guess.
It boils down to something fairly simple. Pakistan was committing genocide to the tune of roughly 90K civilians a day. Why was the U.S supplying that country with weapons while threatening another country trying to stop the genocide?
A simple question deserves a simple answer. It was in the U.S’s national interest to support Pakistan against Russian backed India. The U.S could care less if it’s ally(or for that matter anyone not affecting U.S interests) was committing Genocide. But if a U.S adversary does the, then one could expect a very different response. Once again, it’s all about national interests.