As a free / open source software developer, why should I care? In what situations would I want to make sure that a proprietary software vendor could embed my free software into their proprietary product?
> As I said, I am not only pro-copyleft, I am also pro-permissive licensing. The difference between these is tactics: the first tactic is towards guaranteeing user freedom, the second tactic is toward pushing adoption. I am generally pro-freedom, but sometimes pushing adoption is important, especially if you're pushing standards and the like.
Outside of that situation: because they might give back changes to your software, even if they don't free the rest of the code. Of course, this might be a good argument for the LGPL.
Your bank can't open source it's banking system. Probably in a literal we-lost-the-source-code-in-1993 way.
Wait, what?
The Linux kernel is GPL and is used in countless proprietary applications.
Actually, you can make changes to GPL software without releasing those changes. The main restriction of the GPL is that if you distribute the software, you have to distribute the source too. But you have the freedom to do any changes and keep them to yourself without distributing anything.