Praise be to Allaah.
The response that you describe is wrong, and the people’s evil actions cannot be justified. Allaah says (interpretation of the meaning):
“And if you obey most of those on the earth, they will mislead you far away from Allaah’s path” [al-An’aam 6:116]
Rulings on what is halaal and what is haraam are taken from the Book of Allaah and the Sunnah of His Messenger (peace and blessings of Allaah be upon him), not from what people do, because people may be wrong or they may be right.