Currently we are a level 3, in a level 4 you can't ignore false positive.
In a level 3 you can, since the driver is the "net safety system", in a level 4 you don't have the net, so you can't discard information.
You can't have a unreliable sensor, since you can't drop the info it give you.
Make that the lidar see what a camera can't ( make it night and poor illumination ) but you think it could be a false positive since the camera and radar didn't see it, so you discard the data.. so what the point? you have a good sensor, that gave you good info, but you can't use it because it's unreliable..
Put the other case, you choose to do 2 ot of 3? ok, let's say that the radar has some false-positive and it's raining, so the lidar also has false-positive ( and this is sure. it will. it will not be a strange-coincidence ), so you act, but it was a false positive, then you are in the *sugar*. What good had lidar done to you? nothing.
You simply can't have an unreliable source, if you just say "ok, but the radar can have a false-positive", then you are wrong.
If a sensor can have false-positive, then it's less likely but even 10 sensor can have false-positive at the same time, using more sensor doesn't solve the problem, it only reduce the probability but it cost the double.
The good (and only) way is to solve the problem so you don't have false-positive.