The difference between this and seatbelts is that with the LED, you are trying to prevent someone from maliciously using the camera, while with seatbelts you are trying to give everyone the ability to be safe should they choose to do so.
And regardless, the ability to defeat it should be a factor in determining whether or not it is worth regulating, even if it isn't the sole factor. The combination of having the LED both easy to defeat, and having very limited usefulness, make it not worth regulating.