This is the exact formulation of the argument before computers beat humans at chess, or drew pictures, or represented color correctly, or... Self driving cars will be solved. There is at least one general purpose computer that can solve it already (a human brain), so of a purpose built computer can also be made to solve it.

In 10 (or 2 or 50 or X) years when Chevy, Ford, and others are rolling out cheap self driving this argument stops working. The important thing is that this argument stops working with no change in how hard C to Rust conversion is.

We really should be looking at the specifics of both problems. What makes computer language translation hard? Why is driving hard? One needs to be correct while inferring intent and possibly reformulating code to meet new restrictions. The other needs to be able to make snap judgments and in realtime avoid hitting things even if it just means stopping to prefer safety over motion. One problem can be solved piecewise without significant regard to time and the other solved in realtime as it happens without producing unsafe output.

These problems really aren't analogous.

I think you picked self driving cars just because it is a big and only partially solved problem. One could just as easily pick a big solved problem or a big unstarted problem and formulate equally bad arguments.

I am not saying this problem is easy, just that it seems solvable with sufficient effort.