You can and should have both. It's a form of defense at depth.

The theory of comparative advantage (David Ricardo) means it's worth specializing. But the counter argument (local resiliency) is also important -- but it may mean less efficiency in the short run, as a kind of investment against risk.

All that is fine, but it opens up the opportunity for short-sighted decisions (basically a mercantilist view that exports = good and imports = bad) like tariffs to protect local mfrs (which removes incentives for them to be efficient).

In short, like everything in life, there's not a sharp decision.