Modernity hated ambiguity and mystery : there always had to be only one correct "clearcut" answer --- not a diversity or variety of maybes, sometimes and sort-ofs.
A clearcut binary division between the right answer or the wrong answer, the right method or the wrong method, the normal individual and family or the deviant individual and family.
Not unexpectedly then, Modernity also wanted a small, clean, clear, pure, gene pool.
And Modernity's eugenic-dominated Science was glad to help.