> But if all we're talking about is "mining" websites like HN for topics and then creating original content that covers those topics in a different format for a different audience... where's the issue?

Plagiarism, generally. I really enjoyed the semi-recent hbomberguy video on why it matters, and a later response (from another channel) on "The Somerset Scale of Plagiarism" for a more rigorous explanation of what the different kinds of "content reuse" can be. Those are generally where my current model of plagiarism comes from.

A specific concern would be the inaccurate telling of information that isn't understood. A video saying, "Here I will summarize this HN thread," is perfectly ok, and a good thing. A video saying, "Here I will tell you how $thing works," should be well researched and cited. Doesn't matter if the content's entirely from an HN thread for from 40 different SEO farms, it's low-quality content and it's wasting everyone's time at best, and probably actively misinforming people. (Because how true and complete is information gleaned from HN comments anyway?)