It was clear that if I didn't spend the rest of my life concentrating on string theory, I would simply be missing my life's calling. - Edward Witten

Good wrong ideas are extremely scarce... and good wrong ideas that even remotely rival the majesty of string theory have never been seen.

In Newton's day the problem was to write something which was correct - he never had the problem of writing nonsense, but by the twentieth century we have a rich conceptual framework with relativity and quantum mechanics and so on. In this framework it's difficult to do things which are even internally coherent, much less correct. Actually, that's fortunate in the sense that it's one of the main tools we have in trying to make progress in physics. Physics has progressed to a domain where experiment is a little difficult... Nevertheless, the fact that we have a rich logical structure which constrains us a lot in terms of what is consistent, is one of the main reasons we are still able to make advances.

I don't think that any physicist would have been clever enough to have invented string theory on purpose... Luckily, it was invented by accident.