I would argue that’s not necessarily the case - see slavery, caste systems, discrimination etc. In many countries currently and throughout history it’s been perfectly legal to treat the “other” as less than oneself, even up to and including murder and torture.
Also, often laws are created to enforce religious doctrine, which while perhaps morally preferable to those of that religion may be abhorrent to those outside it. (Abortion, burkas/hijab, education restrictions, prison sentencing, drug/alcohol legality, etc)