Copyleft licenses <i>are</i> restrictive as obligations are restrictions. "You must provide a source code to your users" is equivalent to "You cannot use this software if your source code is not available to your users".<p>Freedom is a finite resource in which copyleft licenses take from the developer to give to users. (which ends up at the same point as the article but I prefer wording it this way.)
I disagree with the title, it feels like arguing on a technicality. Obviously they are restrictive because they make you do something.<p>As the author points out, there are two axes, freedom of use and obligation. Copyleft has high freedom but some obligation. When collapsed to one dimension that obligation is a restriction.<p>Licenses like MIT that require sharing a notice would have high freedom and a minor obligation.
CC0 or unlicense would have complete freedom and no obligation.
This article paints copyleft software as something fairly disjoint from corporate software, however in my experience these are not mutually exclusive. If you look at the kernel's howto for new development[0], it seems fairly focused on the reality that a majority of people walking in to the linux project are doing so on the payroll of some company. For some guy in his 20s who is a bit late to the party, and not being helped out by some corporate arm, the Linux kernel feels like this completely unapproachable monster. In other words, without knowing someone ahead of time it seems impossible to be active in the community. The source is available sure, but that doesn't mean the code isn't corporate.<p>Copyleft licenses often need a lawyer in the room to figure out what can and can not be done, they are complicated legal documents. My preference for MIT is to allow software to spread in a way unencumbered by the access to a license lawyer.<p>[0] <a href="https://www.kernel.org/doc/html/v4.16/process/howto.html" rel="nofollow">https://www.kernel.org/doc/html/v4.16/process/howto.html</a>