The kind of perpetual motion that violates thermodynamics is the kind that can do useful work, i.e. that you can get energy out of, without putting any energy i

The kind of perpetual motion that violates thermodynamics is the kind that can do useful work, i.e. that you can get energy out of, without putting any energy into it. So it violates conservation of energy. A planet in orbit, or a spaceship like Voyager travelling through the galaxy, is in perpetual motion, but if you try to harness that kinetic energy, you'll slow it down.