Note: the opinions expressed here are solely mine. (Duh)
Something that I take rather seriously is the copying and redistibution without credit (intentionally or otherwise) of free software, i.e. plagiarism.
There's a huge difference between something being in the public domain and being free and open source. The latter has a license, for one, and the purpose of it being under license is to preserve the rights of the author(s) to their work(s) but some people either misunderstand or ignore that distinction.
There's a huge difference between something being in the public domain and being free and open source.
Now it must be said that most people generally abide by the licensing of free software projects but I've come across and been personally affected by instances when folks simply copy some works and remove or replace the original license during redistribution and modification (usually unbeknownst to the original author) and thereby take credit and this is unconscionable in my view. People put free software licenses on their works in good faith and there is a general expectation that the larger community also acts in good faith when modifying works but the onus is still on us to exert our rights otherwise the license loses its effectiveness and free software is lesser for it.
All that said, in my experience this kind of plagiarism occurs on a pretty small scale on projects with one or a few authors—no one's out there copying the entire Linux kernel and passing it off as their own work—but if we are to be good advocates of free software we also have to be guardians of it regardless. We need to hold plagiarists accountable for their actions or at least call them out on it.