What does Peter Singer say about the history of liberation movements?
They tend to become narrower in scope … zeroing in on the exact class that deserves moral consideration.
They tend to become wider in scope … with people learning to apply moral principles to groups previously not considered.
They tend to become more discriminatory … giving fewer and fewer rights to the less privileged.
They tend to discover that the original concepts in the past were superior and it is a mistake to veer from traditional wisdom.