I kinda like this viewpoint. If a war is so dire, so needed, and the nation is at the brink of destruction, people will willingly join.
But there are other reasons in conscription than just a shortage of people for the army. There is also the dissipation of the surplus, when suddenly at the last minute the conscription system is flooded with waves of volunteers, it will immediately be overloaded because, first, there will be too few people to train, because most of those who know will already be at the front, and second, there will be too few weapons, because professional armies are not famous for holding mobilization stocks and which conscript armies have.
Why? Because the conscript army on a peacetime basis is scaled down to 1/3 the volume of the professional army. The whole point of it, is to develop mobilization and fill vacancies with conscripts, much earlier trained, already in peacetime! Thanks to this, it is not necessary to cut off part of their training to the most basic skills in order for the front to get immediate replacements, because they have these skills hammered into their heads.
The problem with the national volunteer spurt, precisely lies in the fact that most often it fails to take full advantage of it, and such people will be trained much worse than conscripts. Because the trainers must immediately push them out of training after they finish the basics to make room for the next ones.
If instead, you build a system that teaches the necessary skills in peacetime. In the event of a W, such volunteers along with mobilizers will be much more useful. Because you only have to test their skills in a refresher course and, if you are building a new unit from scratch with mobilized and volunteers, lump them together. Which will take much less time than if you have to train them from scratch.
This approach, in a way, is counting on the luck and stamina of the professionals to hold the line until the new forces arrive. This approach is only viable as safe if you have a position like America did during both World Wars. In other cases, it is as in the first sentence.
Forcing countries that are, in the event of war, immediately in conflict on their territory to take this approach. This is an example, dishonesty and naiveté. A wrong approach that will get many more people killed. It would even be immoral for them to do so.
But hey! They're not being forced by force to serve in the army! After all, that's great, right?
And the fact that because of this attitude, many of them will be killed during the war is none of our business./sarcazm mode
As they say, prevention is better than cure.