I get what you are saying but if the content is identical you won't be able to tell them apart either way.

For example imagine if you and a friend are buying the same anime blu ray, you compare them and you don't notice a single difference but a month later the seller tells you that yours is a fake (you would have never noticed otherwise) would you really care that much ?

Also there is still a difference with torrents, the torrented version comes only in digital form you won't have an disc or a blu-ray case. And most of the time there isn't a blu ray menu its just the video files ripped. (not even mentioning the security risks if you don't know what you're doing)