I cannot see any correlation between weapon exports and demographics.
Experts in foreign affairs could write tons of essays about the benefits of designing, manufacturing and exporting weapons in this world.
It's not just the little money it stands for in your trade balance. It's a lot of influence because countries that buy weapons from yours somehow depend on your own.
That's why the US has always regarded France as an 'ungrateful' ally.
We don't want to depend on them too much. For example, we can design our own nukes and nuke your ass whenever it would be necessary.
The whole process of designing and producing nukes is our very own in this country. It costs some taxpayer money, but at least, we are fully independent in that respect.
That's not the case of Britain that actually relies on the US even when it comes to their own safety.
As for demographics, well, Africans are very much of the future, whether you like it or not.