Not long ago, no one would consider earth is round.. or that planes can fly.. plenty of car tires have been mounted on motorized 2-wheel vehicles and millions of miles have been ridden on them. No indication that incidents are more likely riding with car tires mounted on the rear wheel.
As someone who has experience riding with a car tire mounted on the rear wheel, I can say that it is safer in most applications when operator knows how to ride, just as any tire, moto specific or not. Just as any new tire mounted on a vehicle, moto or car specific, learning curve of vehicle handling is to be expected.
IMO, liability is for those who depend on manufactures rather than riding skills.
If anyone is interested in my experience of riding with a car tire mounted on the rear wheel, I'm happy to share.
But to debate about this topic without actual experience is like telling someone the riding a motorcycle is dangerous shouldn't be attempted while never ridden a bike themselves.