Same thing with language, really. The word "red" has no inherent meaning beyond social consensus. To the extent that you want to be able to communicate with others using a particular language, you have to adopt the agreed-upon meanings.
So to the extent that we want to communicate or to function in a particular society we need to adopt the local meaning of language or social mores. If you don't care about communicating, or are fine with the potential sanctions that come with violating social mores, then you can ignore things.