> But the only assumption required is that someone uses your product instead of the free alternative. He might have higher quality software, but he does have less software freedom.
No, he has the same software freedom -- he has the freedom to choose to use and/or modify the free version and any free derivatives people have chosen to make, and the freedom to choose to use the non-free derivative, with perhaps less freedom to modify it.
If anything, he has less freedom when the creation of non-free derivatives is prohibited.
Once he becomes locked in to the non-free platform, his is not free to modify the platform he relies on and is instead required to migrate to a completely different platform in order to make (potentially small) modifications.
By this logic, OSX is free software because I have the freedom to choose Windows instead.
I'm not advocating for the prohibition of non-free derivatives, but the position that adoption of propriety software doesn't reduce software freedom is ridiculous.
You "by this logic..." is wrong because the post you are responding to doesn't make any argument about what is a piece of "free software", it discusses what the effects on software freedom are of the exercise of rights under particular free software licenses.
Freedom is the power to make choices rather than suffer external dictates. If a particular piece of free software exists, the existence of non-free derivatives doesn't reduce anyone's freedom, as they are free to choose the free software.
No, he has the same software freedom -- he has the freedom to choose to use and/or modify the free version and any free derivatives people have chosen to make, and the freedom to choose to use the non-free derivative, with perhaps less freedom to modify it.
If anything, he has less freedom when the creation of non-free derivatives is prohibited.