What the poster seems to have meant is that LIDAR is essential hardware. Which is not some universal truth, so it is they who should justify it.

Visual cameras can be blinded fairly easily - even high-end cameras - simply point such a camera at the sun and try to make out a cloud in the sky. If Tesla were using true high-dynamic-range cameras (e.g. Oversampled binary imagers) then I would be more confident - but Tesla isn't saying that they are - and if they really were they would definitely boast about it.

LIDAR also does work great in the rain - provided you have multiple LIDAR units (e.g. Ford's snow-proof sensor array: https://qz.com/637509/driverless-cars-have-a-new-way-to-navi... ).

What I like about LIDAR is that it will never give you false-negative data regarding object proximity (i.e. it will never tell you an obstruction in the road is not there) but visual-only cameras can be fooled very easily and definitely can give you false-negatives regarding road obstructions.

It seems inherently less safe to rely on a more homogeneous sensor array: conversely it makes sense to use as many different types of sensor as possible to ensure your design isn't susceptible to being brought down thanks to a weakness in your predominant sensor type.

Lidar is absolutely useless for level 5 autonomy given that doesn't work in "bad" weather. It may be useful for level 4 autonomy but for sure it is not necessary even then. Source: no car driven around the planet at the moment has any lidar apart for testing purposes.