This is a huge burden on the electrical grids, and Tesla or EV's get to hand that problem to someone else.
The only way this makes sense at scale is if we had nuclear power, and charging was done at night.
They don't exactly get to push it onto someone else. Large loads like this come with demand charges. In some areas, they might be $5/KW, in others I've heard of >$10. A single megacharger would be $5-10k on top of the actual energy used.
It is high enough that I'd expect them to start thinking about battery buffers at charging sites to mitigate the cost.
That already happens at a smaller scale, with things like Freewire.