Bradley Kuhn's talk at LibrePlanet 2017 on enforcing the GNU GPL at the Software Freedom Conservancy explains the challenge of enforcing the GPL against today's violators.

The Conservancy provides various kinds of administrative services for free software projects, while promoting the free software ethical ideals and the use of copyleft. It also does GPL enforcement for Linux and some other non-GNU, GPL-covered software packages. In doing so, it undertakes a crucial job.

The Conservancy, like the FSF, follows the community-oriented enforcement principles that adopt the goal of bringing redistributors into compliance, so that users will have the freedom they are supposed to have. This implies starting with private conversations in a civil tone, and taking legal action only as a last resort.

However, as I wrote long ago, the GPL is not Mr. Nice Guy. When a redistributor obdurately persists in violating the GPL, a lawsuit may be the only way to make it respect the freedom users are entitled to. In this last-resort situation, going to court is justified if it's necessary.

The FSF urges people to become supporters of the Conservancy.