The alternative is to require the car to be able to see everything all the time and treat gaps in its view as "might be something there", but doing that in the dark is really only possible with LIDAR at the moment.
Not all humans manage to do that, and they're liable if they crash into some other car. Loose their insurance and cannot drive anymore if they do it too often.
Which seems a good enough reason that we need to add regulation that these vehicles must have multiple redundant sensors that can operate at any permutation of sunlight/night/rain/snow/fog.
Radar can also see at night, but has poor resolution. Sonar is good at looking through fog but may be unreliable at highway speeds. Lidar really seems like the only viable option here. Maybe even lidar + radar.
I think it's interesting that Elon Musk always says we don't need lidar because it's a visual world. Lidar is a visual sensor. Just an active one.
We manage to get away with 2 2D sensors, that can actively move around and we have freaking 3 billions of neurons with extensive knowledge of the physical world. We are not giving back only a 3D approximation due to the angle difference between our eyes - we also semantically analyze it, knowing what a car, a tree, the sky, etc are, with their usual dimensions in directions where we don’t even see it.