Sure, common practice doesn’t mean it’s automatically right but it is an indication that it’s generally accepted for reasons that may be valid. So it’s reasonable evidence to cite, and is a method of explaining that your argument now has to account for the general case.
I partially/mostly agree, I think it's more of "it's good enough because it's either good or it's close enough to not bother speaking/complaining/doing anything about it". Eg targeted ads are accepted, but banning them takes massive effort and "people can use ublock anyway". But yeah that's splitting hairs.
