Electric cars do need to be sustainable, which is going to be a problem. You've actually brought up a good argument with cobalt. However the same argument could be had for a lot of things, like current cars which require gas, which has to be found. The US is currently pumping a lot of oil out of the ground. How long can that last?
The US has 36.4 billion barrels of proven oil reserves.
The US is producing about 9 million barrels a day. Which is 3.2 billion barrels a year. At this rate the US will have gotten through its proven reserves in a little over ten years.
Now that doesn't mean the US will run out of oil. Proven excludes oil that hasn't been found.
But at some point it is going to start running dry.
The US has how much cobalt, 23,000 metric tons?
A Tesla battery needs 140 lbs of cobalt
We have just enough of the element, cobalt, to make 360,000 Teslas!
Now, tell me, what is more sustainable. Using an Element in a luxury car that does not work in the extremes of climate or building our nice modern practical organic fuel burning cars?
Looks like we run out of Cobalt long before we run out of Oil.