How could people back in 50's and 60's have been so cruel?

I read a book named The Girls Who Went Away and it was so sad. During this time period girls who became pregnant outside of marriage was labeled a slut and was coerced to give her baby away. http://books.google.com/books?id=FFmvu14Tz5MC&printsec=frontcover&dq=the+girls+who+went+away+ann+fessler&source=bl&ots=nuvkIOVjNM&sig=z5fO89UFlcsAxUu7W9CKb1dZ0rQ&hl=en&ei=N6QxTMewIMPflgfx0J3jCQ&sa=X&oi=book_result&ct=result&resnum=5&ved=0CCoQ6AEwBA#v=onepage&q&f=false These girls were not sluts some even became pregnant after having only one time.