Appeal to tradition

Appeal to tradition (also known as argumentum ad antiquitatem,appeal to antiquity, or appeal to common practice) is a common fallacy in which a thesis is deemed correct on the basis that it is correlated with some past or present tradition. The appeal takes the form of "this is right because we've always done it this way."

An appeal to tradition essentially makes two assumptions that are not necessarily true:

The opposite of an appeal to tradition is an appeal to novelty, claiming something is good because it is new.

...
Wikipedia