“Plagiarism is the deliberate attempt to deceive the reader through the appropriation and representation as one’s own the work and words of others. Academic plagiarism occurs when a writer repeatedly uses more than four words from a printed source without the use of quotation marks and a precise reference to the original source in a work presented as the author’s own research and scholarship. Continuous paraphrasing without serious interaction with another person’s views, by way or argument or the addition of new material land insights, is a form of plagiarism in academic work.”
You can read more on it here if you like.

I think you missed the “pro-plagiarism” argument all together; it is not about having an original thought that had never existed before, but about being pro-knowledge/pro-community. For example, Even though Thomas Edison is well known for creating the light bulb, he was actually not its inventor. The “light bulb” itself had been around for some time; Thomas only invented the first practical light bulb. If Thomas Jefferson was not required to list every person who ever added to the light bulb, why should society care if I like your idea, but want to change it a bit to make it my own? Sure corporations may get a hold of your idea and use it in their next commercial, but you should be entitled to the same rights. The idea is that you can also take from the corporation, it’s a communal thing.

I’m personally unconvinced by pro-plagiarism arguments, because I think they often mischaracterize plagiarists as free thinkers who value ideas more than the “brand names” by which those ideas are presented.

From what I’ve seen, those who plagiarize most often–and by these, I mean advertising executives, commercial television producers and the like–do so because they have no regard for ideas or for intellectuals. To them, an idea is merely something to provide “content” to which commercial ads, their real message, can be attached. The person who created the idea is beneath their contempt in a world where personal worth is judged on the sole basis of financial success.

Even if you believe that nobody ever has an original though or an innovative idea, attribution of sources not only pays them due respect, but provides metadata which may help the reader determine how reliable your ideas are.

Finally, those who argue that all ideas are based to some extent on ideas created by others miss the point: Plagiarism isn’t the act of merely basing one’s ideas on another’s. Plagiarism is presenting someone else’s ideas, word for word, as though they were your own.

If you’re truly unable to generate an original thought, then at least save yourself some trouble and embarrassment–paraphrase.