This isnt about spying and the 123 agreement is not another 007 movie. The 123 agreement is to relax some sactions US has imposed on India and to allow India to have their fair share in world market to purchase nuclear technology and fuels for peaceful purposes like energy.
There are benefits for both parties. For India its to suffice the huge energy appetite and for US it is to survive their economy.
India along with China and Japan hold a lot of dollars in their iron chests. If it is diluted little bit then US economy will crash. Secondly India is becoming a major player in the world both economically and geo-politically. Having India as their ally will benefit US in the long run. China is a country that they cannot trust. Every American knows that they will have a war with China one day.
So its in the mutual interest of both countries that the 123 agreement has kicked off. Its only the minute details on which both parties are worried about. One of them being the transperancy of purchased fuel being used for energy generation and second one being spent fuel usage. US is scared that India will use the spent fuel for developing nuclear weapons. The agreement started with India being required to sign NPT but thats under the table now. Its not a pre-requisite anymore.
Countries like France and Russia are also supporting the agreement because its not a compulsion for India to purchase fuel from US alone. We can buy fuel or technology either from Russia or France.