It's Gary Marcus "neural networks don't really work" suddenly discovering they do, and literally trying to shut down research in that area while keeping his prefered research areas funded.
We know a bunch of the people whose names are on the letter didn't sign it (eg Yann Lecunn who said he disagreed with the premise and didn't sign it).
I'm so offended by the idea of this that I'll personally fund $10k of training runs myself in a jurisdiction where it isn't banned if this ever became law in the US.