being supported by cultural norms is worse than being supported by law. Laws can be overturned by a stroke of the pen. Cultural norms still persist after the law is overturned. Case in point: black racism and prejudice in the USA.
Cultural norms typically dictate laws and not the other way round. Case in point: The US constitution granted Women right to vote on August 26, 1920 when the Nineteenth Amendment was adopted. And no, it did not happen with a "stroke of a pen". The movement began in 1771 and their rights finally enshrined in the US Constitution in 1920 (~150 years).
Are you suggesting that the current situation for blacks is worse than when there were Jim Crow laws? When racist laws are in place, there are also cultural norms that exist with them.
It's better, but problems obviously still exist.
I didn't disagree with that. The point is that when there are racist laws, the situation is strictly worse than when there are only racist cultural norms because the former does not exist without the latter.