I think the theory and belief in god has caused massive amounts of suffering, pain and war over the centuries, and that will massively negate any benefits to individuals from lengthening life and improving happiness.

From the use of Latin in English churches to keep the masses ignorant and persuade them to keep toiling in the servitude otherwise they go to hell, to more modern day instances such as the Catholic/Protestant conflict in Ireland and the jihad against the west.

To complete my compelling argument, I will reference the great encyclopedia of our times, Family Guy. In the parallel dimensions episode the dimension without god is the most technologically advanced and educated, as the repression of religion never happened. I think there is more than a grain of truth there.