More than 100 years ago Swami Vivekananda gave this talk in Madurai.
“There was a time in this very India when, without eating beef, no Brahmin could remain a Brahmin; you read in the Vedas how, when a Sannyasin, a king, or a great man came into a house, the best bullock was killed; how in time it was found that as we were an agricultural race, killing the best bulls meant annihilation of the race. Therefore the practice was stopped, and a voice was raised against the killing of cows. Sometimes we find existing then what we now consider the most horrible customs. In course of time other laws had to be made. These in turn will have to go, and other Smritis will come. This is one fact we have to learn that the Vedas being eternal will be one and the same throughout all ages, but the Smritis will have an end.”
“The essentials are eternal, the non-essentials have value only for a certain time; and if after a time they are not replaced by something essential, they are positively dangerous. I do not mean that you should stand up and revile all your old customs and institutions. Certainly not; you must not revile even the most evil one of them. Revile none. Even those customs that are now appearing to be positive evils, have been positively life-giving in times past; and if we have to remove these, we must not do so with curses, but with blessings and gratitude for the glorious work these customs have done for the preservation of our race.”