Comparative advantage has its dangers. If you let one of your native industries die and become completely dependent on imports of that product, what would happen if your supplier suddenly decides to stop trading with you? (Maybe they had a natural disaster, maybe civil war broke out over there, or maybe they're pissed because they feel your country has been oppressing people of their religion.)
If the product is vital to your country's survival, then you'll have to ramp up production of it incredibly fast (which may be difficult) or you may be forced to invade the other nation in order to take control of their industry - which would probably end up with many deaths on both sides.