Legally speaking? https://en.wikipedia.org/wiki/Reasonable_person

Any American who likes Tom Petty.

I mean mainstream American society of secular to moderately religious people, as opposed to ultra-religious minorities such as ultra-Orthodox Jews or Old Order Amish

I mean the term quite broadly and inclusively, since many of the big divides within American society (ethnicity, race, politics, class) make a relatively modest difference to fertility rates, and those differences appear to be shrinking over time

SWM