I understand that, my point is that arbitrarily assigning credentials to a person and placing those credentials before the argument is ad hominem. It's putting the emphasis on the person, not the argument. It's also not useful. There are many examples of people who don't have traditional "credentials", but are well informed and make well thought out arguments. There are also a lot of examples of "experts" who can't form a proper argument on a subject at all. So credentials are more or less meaningless. What isn't meaningless is the content of someone's argument.

To discount someones argument just because they don't work in the industry is pretty well pointless. You aren't limiting yourself to only well informed arguments that way, but you are excluding many well thought out arguments from outside of the space.

tl;dr: "Credentials" are meaningless and arbitrary, it's the content of an argument that matters, and how well or misinformed the argument is. It only hurts the dialogue to discount certain opinions based on perceived credentials.