This is the Pascal's wager of stock arguments.

It omits a lot of other scenarios that increase the actual risk of betting on Tesla...

Self-driving becomes a commodity and so there's no unique Tesla win.

Self-driving becomes something only Tesla controls but (in the fleet/rental model) doesn't bring back returns to justify this investment because of extremely high capital, maintenance, regulatory, or other costs.

Self-driving becomes something only Tesla controls but (in the personal-owner model) doesn't bring back returns to justify this investment because it doesn't motivate the entire world to splash out on new vehicles overnight and also doesn't override other existing biases/preferences.

Self-driving is won by someone else (maybe someone with less religious views about Lidar, say) and Tesla no longer can even sell that promise.

Those are just the ones that occur to me in a few minutes!