I don't "get" why we're arguing about it at all - we don't need to. In 2016 there exist authentic, functioning hunter gatherer societies and it is possible to witness and document them.
Here is some witness and documentation:
http://www.vladsokhin.com/work/crying-meri/
... perhaps scroll down to the photos of women being cut open and burned at the stake for witchcraft, or the mutilated survivors of tribal justice.
Looks like a real party.
As far as measuring happiness, one method would be levels of stress hormones in the blood.
Infectious diseases, though, are very much a product of agricultural society, as is starvation/famine. We might be living through the century (or possibly, have just lived through the century) where our technology finally enables us to fix these two problems caused by our ancestors' conversion to agriculture.
[0] http://www.anth.ucsb.edu/faculty/gurven/papers/GurvenKaplan2...