That leaves you with an army consisting entirely of incel failures and monstrous sociopaths (with significant overlap between the two groups). Armies should reflect the leadership in their wars so that decisions of military and social governance are made with skin in the game. An army of mercenaries and/or incels has all of the problems of a state running an army of killer robots, in that if consequences and military disasters don't affect anyone that anyone cares about then there's no reason a brutal war wouldn't just keep getting waged indefinitely, especially if it's an imperial, colonial war waged far from domestic eyes.
For the most part, modern states put up at least a pretension of democracy. The government is charged with its duties by its society, and discharges its duties according to society's guidelines.
In democracy, there can be no legitimate differentiation between being a participant in society and being in the position of leadership and authority in the state. There can be no difference between a legitimate military target in a war and an illegitimate civilian target. A suicide bomber who blows up a democratic society's public bus in a war has attacked the enemy's head of state. "But the individuals in democracies are often overruled by more powerful rivals"–yeah, the same shit happened historically to leaders in monarchies and theocracies, welcome to governance. And the democracies of the world are extremely fond of exercising this standard against non-democratic rivals, with names like Dresden and Hiroshima making that point perfectly clear.
The people and society at large in a democratic state are part of the wars of democracies, they are participants in it and they are legitimate targets of enemies within it. Wearing a uniform and operating a resupply station for a period during a democracy's war does not change that in principle, it just brings that already-existing reality to the surface and makes it uncomfortable.
That discomfort is, in and of itself, a good thing.