That's an easy question. Make software that combines GPL and non-GPL code. GPL, due to it's political nature, makes it purposedly hard to inter-operate with software that does not carry its philosophy. Maybe it's good for philosophy (which I am yet to see any serious proof of, but maybe I'm just ignorant and it is going great there) but certainly isn't good for me, even when I can reuse the components separately.
That's not true. You can combine GPL and non-GPL code, as long as the non-GPL code is compatible with the GPL. Pretty much all of the popular free licenses are compatible with the GPL.
I think there's a widespread misconception that you have to relicense code in order to combine it with the GPL. You don't. The code can retain its license, because its license allows it to be used with the GPL.
Saying that you have to relicense MIT-licensed code under the GPL is like saying that you have to grant a special proprietary license for Apple if they want to use your code in macOS.
> You can combine GPL and non-GPL code, as long as the non-GPL code is compatible with the GPL.
That's a pretty big exception, which reverses your conclusion. It's like saying "not true not everyone can buy Lamborghini Aventador - everybody can, as long as they have half a million dollars to spend!" That's kind of the point that turns your "not true" into false.
> Pretty much all of the popular free licenses are compatible with the GPL.
Just look at the "GPL compatibility columns". Even GPL2 is not compatible with GPL3 without a special "or later" clause, which is all too easy to miss.
> The code can retain its license, because its license allows it to be used with the GPL.
But if you want to distribute the mix, you'd have to abide by GPL conditions.
It's not. Most of the anti-GPL free software advocates are using compatible licenses, such as the MIT or BSD licenses, and they are already following all of the conditions of the GPL, since they are distributing source code.
> But if you want to distribute the mix, you'd have to abide by GPL conditions.
Almost everyone is already abiding by the GPL conditions when they are distributing MIT-licensed code. The only real concern about violating these conditions is to not distribute source code. If you have no intention to distribute non-free software, you should have no concern with the GPL.
I just cannot understand, try as I might, why anyone would have a problem with the GPL while at the same time eschewing non-free software. If you are already doing as a matter of course what the GPL is asking you to do, why do you object to being told to do it?
