1. User wants to use my GPL'd library in their application. Their application is released as source code under the 3-clause BSD license.

2. User sends me an email asking me to change my library's license to MIT or 3-clause BSD so their open-source app can use it.

3. I reply with the longform equivalent of "u wot m8?"

4. They reply that if I change my license to MIT, they will be able to "relicense" it to 3-clause BSD and use it as a dependency in their application's build script.

5. I explain that they don't need permission to just depend on a library, since they're not distributing any of it. And besides, if they did include some of my code in their tarballs, they still can't change the license because they don't own the copyright.

I suspect this stems from the same sort of pseudo-religious copyright knowledge that leads to "no copyright intended" disclaimers on YouTube. Lots of people grew up in the era of Napster and copy-pasted MySpace javascript, and never really gave much thought to how copyright actually works.