I think, in practice, that your example still doesn't work.
First of all, that's an argument against not divulging trade secrets, rather than forbidding the worker from working in the same general field. There aren't a lot of cases where somebody can reproduce an important new product from scratch without bringing over mountains of documentation.
If somebody can take the bare idea, go to a competitor, reproduce a product, and get it out to market faster than the original company, then the previous company was probably doomed anyway. This does happen from time to time but let's face it -- this is a GOOD thing.
First of all, that's an argument against not divulging trade secrets, rather than forbidding the worker from working in the same general field. There aren't a lot of cases where somebody can reproduce an important new product from scratch without bringing over mountains of documentation.
If somebody can take the bare idea, go to a competitor, reproduce a product, and get it out to market faster than the original company, then the previous company was probably doomed anyway. This does happen from time to time but let's face it -- this is a GOOD thing.