Yeah, and I think unpacking that helps clarify the issue, because who exactly is going to be doing the plagiarizing? Like: as with everything, people with more resources and a higher social position can and will do more plagiarizing, simply because they have more chances to do it and are less likely to be punished for it. As hbomb points out repeatedly in the video they're ALREADY the people who do most of it; ltrl the first anecdote he covers, that of ABC ripping off Ellison's Brillo story, is an example of this. Plagiarism, like almost anything, is a systemic problem.
And, when your society is a hierarchical one like ours where Fame(Credit for doing a thing) grants Success and Success grants Authority, tolerating it makes everything in your society shittier. Again, as hbomb repeatedly shows, it's much easier to steal someone's work than to do similar work so, in a society where plagiarism isn't considered a big deal(or is seen as proof of one's laudable Cleverness/Ruthlessness), you're going to naturally see less interested, less ethical, less careful, less attentive, and less exacting people rise to the top through their plagiarism(and the personal and class abuse it fundamentally is since higher status people steal from lower status ones), which is in itself going to cause problems. They'll be less able to handle the responsibilities they've gained; they'll be less able to actually do the job and more prone to fucking it up; they'll be more likely to abuse those they've been given authority over because they fundamentally do not care about being ethical people. A person who cares more about wealth and status than doing a good job will be bad at their job. In professions like journalism and academia you might see fabricated and inaccurate information passed off as the truth(again, something hbomb shows these plagiarists repeatedly doing), which just basically negates their purpose. In professions like law and politics, the opportunities for misrule open to unethical people are even more destructive. The social convention against plagiarism(and it really must be understood that this IS a Social Convention; plagiarism needs to rise to the level of copyright theft before courts will even touch it and they'll rarely punish anyone even then as hbomb notes at the beginning of the video) acts as a stopgap; to incompetents breaking something that hurts THOUSANDS, and to abusers gaining the authority to commit worse abuses.
But the thing is: even WITH that social convention, we ALREADY SEE Examples of these problems because too many people with a say in how our institutions are staffed and managed care MORE about hierarchy and nepotism(rewarding their friends and punishing people they dislike) than they do honesty, fairness, competence, and justice. Full Professors leveraging the precarity of their grad students' situation to extort their work from them was an open secret in USian academia through the 90s and 00s(probably still IS given the academic jobs situation has worsened since then), and particularly bad with "Celebrity" academics(ie: profs who are also tv talking heads). Male bosses stealing the work of their female secretaries(and white bosses stealing the work of their non-white employees) was so common it was a running joke in US society from the 50s to the 00s, as was their leveraging of it to extort wages, work, and sex. Plagiarism, fundamentally, is a gamble of power; a roll of the dice that your theft won't be noticed or punished because the ones you steal from are too lowly or obscure for anyone to know or care about. To plagiarize is to say "the person who did this doesn't matter as much as me" and, no surprise, a society built on the idea that some people matter more than others like ours implicitly encourages it. Is that something we shouldn't care about?
And I guess that really gets to the heart of it because, fundamentally, the question of plagiarism is a question of justice. To say you don't care about plagiarism is to say you don't care about justice, or fairness, or honesty; to say that injustice doesn't bother you, nor does being lied to by authorities. And if that's how you feel Fine, but just know that ALLOT of people aren't going to trust you after that.