I don’t have a legalistic view of the world; I am saying plagiarism is a legalistic concept. For context, I support the abolition of law and of intellectual property. Plagiarism is a particular kind of violation of intellectual property law, and without IP, it makes no sense. You still fail to define a plagiarism outside of the law, and you also fail to define a plagiarism that does not violate MIT/BSD. MIT/BSD both require attribution. You cannot claim MIT/BSD code written by someone else as your own without breaking copyright law.
Ok, in that case your definition is inclusive of things which are not conventionally considered plagiarism. Ghostwriting is commonly looked down upon, but not considered plagiarism. A large part of a non-legalistic definition of plagiarism includes a lack of consent from the original creator; if you take a job as a ghostwriter, you agree to your writing being published under a different name. If I work as a developer for someone who wants to make their own app, say a YouTuber, and they publish the app I wrote as <YouTuber’s> app, most people would consider that perfectly normal and not plagiaristic, since the developer was paid for a service in which it was understood their work would be published under a different person’s name.
You are also avoiding the original question about BSD and MIT, and not explaining why that is plagiaristic. Do you still think they are plagiaristic? If so, how? Given that both the licensor explicitly wanted people to be able to re-use their code in proprietary software (i.e. consent/permission exists), and these licences require attribution (i.e. not only are you not taking credit for it, you are actively naming and crediting the original author).