What changed?
Before the 1970s, liberals had not slaughtered 50 million babies. Once you perpetrate such evil, any mass killing is easy.
Before the 1970s, communism was repellant to most Americans who cherished America and its ideals. Communism says the end justifies the means and killed 100 million people in the 20th century. Once you subscribe to such a system, any mass killing is easy.
When “Thou shalt not kill” is removed from schools and the public square, any mass killing is easy.
What do all three of these pathologies have in common?
Yup, once a society not only legalizes the murder of the most innocent and defenseless within it, but champions it, that society will tolerate and encourage most anything, and that society is doomed.