The freedom in free speech is freedom from restrictions imposed by the state.
Now what freedom from restrictions by the state could "free software" refer to? It can only be the existing intellectual property regime, copyright.
But the GPL depends on the existence of copyright law. It's not just a license that creates a situation which would arise naturally without copyright law.
Sure, without copyright you could not prohibit others distributing copies of your software.
So in this sense, it would be consistent to call a license that grants this right to as many people as possible "free as in speech'" — roughly like this:
(a) you are granted the right to distribute copies of this software or derivatives of it
(b) all derivatives must be licensed under this license
But no more than that.
For such a license, if copyright gets abolished tomorrow, nothing changes. The rights which were explicitly granted are equivalent to the removal of the restrictions.
But the GPL goes beyond that.
With copyright completely abolished the following would be legal, feasible and practical:
- You could use someone's source code, modify it and distribute the compiled binary. But keep the modified source code secret. The GPL explicitly prohibits this, it forces you to share your source code modifications fully if you distribute a modified binary.
- You could do Tivoization. The GPL v3 prohibits this.
So ironically, the GPL depends on copyright. If copyright gets abolished, the GPL would be "defanged". You could legally do more than you can do now.
Again, I'm not saying only the BSD or MIT license are free like in "free speech". It's ideologically consistent to propose a viral copyleft license and make the "free speech" analogy.
But the reasoning behind the GPL rhetorics is still flawed. It expands the definition of freedom to be also free from certain restrictive actions by private actors which they could even do without copyright.