Here’s a favorite quote from the English philosopher who invented Utilitarianism along with Jeremy Bentham:
The entire history of social improvement has been a series of transitions, by which one custom or institution after another, from being a supposed primary necessity of social existence, has passed into the rank of an universally stigmatized injustice and tyranny. So it has been with the distinctions of slaves and freemen, nobles and serfs, patricians and plebeians; and so it will be, and in part already is, with the aristocracies of colour, race, and sex.
When we read this section in my ethics classes I like to ask my students what tradition or custom in today’s society will one day be stigmatized as injustice. Always a good discussion.