I don't think military history supports that view at all.
Countries and armies don't win or lose wars according to how many "decent men" they have. If they did, military collapses would never happen. In reality, outcomes depend on leadership, logistics, morale, training, intelligence, equipment, funding, political support, and whether people believe the government they're fighting for will survive.
The Afghan security forces numbered in the hundreds of thousands on paper and suffered enormous casualties over two decades. Tens of thousands of Afghan soldiers and police were killed fighting the Taliban. Whatever else you think of the Afghan government, it's hard to argue those men simply didn't care.
The problem is that once the state began collapsing, commanders surrendered, local deals were made, supply chains broke down, and international military support was withdrawn, individual courage couldn't compensate for systemic failure. History is full of armies that collapsed despite containing brave people.
Saying "if there were enough decent men they would manage" doesn't really explain anything. It's just taking a complex military and political collapse and reducing it to a moral judgement about millions of people.
You can criticise Afghan society, the government, corruption, or the way women have been treated without claiming that an entire nation's men were cowards. The evidence for that simply isn't there.
If "a country would be free if there were enough decent men" were true, then we'd have to conclude that Iranians (until recent protests), people who lived under the Soviet Union, modern Chinese citizens, North Koreans, and countless others are all cowards because they didn't successfully overthrow their governments.
That's obviously not how political power works. Authoritarian regimes survive through organisation, coercion, weapons, intelligence networks, patronage systems, and control of institutions. Ordinary people can oppose them and still be unable to defeat them.
The fact that a regime exists is not evidence that the population supports it, nor is it evidence that everyone who failed to overthrow it lacks courage.