The ridiculous GPL-only tagging of Linux

Imagine that you release software under a license that is primarily concerned with making sure that modifiable source code is available to all and that no restrictions should ever be placed on derived works. Now imagine that someone takes a huge body of code like this and starts marking interfaces as limited to specific uses and claims that removing those markings is not permitted. How can the code be free for modification and not free for modification at the same time? It’s clear that some of the developers of GPL Linux kernel code discovered that it was difficult doing business under the GPL, but rather than finding a different license more to their liking, they have attempted to add additional conditions to the GPL  – something that the GPL specifically prohibits.