There’s nothing “inherently” wrong with the loss of manufacturing jobs to other countries/overall, if that is what is most economically efficient. I think Peter Schiff is more commenting on government intervention which makes manufacturing in the US relatively less profitable.
It would be better that most/all government regulation not exist and allow the free market to determine where things get made.
I’ve certainly never heard Schiff say we should devalue our currency to make American manufacturing more competitive.