A good overview of the first category for anyone interested.
Basic "necessary but not sufficient" thing here.
The counter-example would be places where armed people are kept under the boot by those in power anyway, where the government is very effective at oppression.
edit: unless you are equating "able to do things that make citizens want to shoot you" with "effective"? I'm assuming you misunderstood, which is the charitable reading.
On a grander scope, notice how Taiwan has not been invaded by China despite their decades of rhetoric. They're armed, the price is high and the move would be risky.
And no you dont just pray at the time you need a weapon and it pops up in your hands. That's not how things logistically work. Also a big part of it is an ongoing cognitive deterrence. That doesnt happen when people dont have them at the present time.
Just like we don't use 'I brake for whales' or this old chestnut:
https://quoteinvestigator.com/2011/10/20/last-tree-cut/
As a basis for any real discussion of environmental policy.