Why is the national security argument not convincing?

Imports are blocked, more often than not to promote and support the domestic producers. There are many arguments by which countries restrict imports like Infant Industry Argument, Environmental Degradation Argument, etc. One such argument is National Security Argument.

Under the National Security/Interest Argument, it argues that a nation can not and must not heavily rely and depend upon other countries for the supply of certain key products like defense machinery, oil, etc. These products are of key and strategic importance to any country.
But, the argument is not convincing enough as if we don't import, it suggests to domestically utilize the limited resources without any efficient technology. This might be even more harmful for the economy. Also, under this argument, countries attempt to restrict the imports of even those products which can't really be called as a national concern. Hence, the argument is not convincing.