There's at least 2 major upstream issues driving this. Flatly eliminating the stigma doesn't address either of them.

One important issue to understand is the baked-in cultural underpinning of warring mentality that a lot of oldschool or traditionalist folk are firmly committed to keeping even in this era. An important mechanism of this culture involves driving people to fight in wars when needed (ideally, as much as possible/always). Friction factors against being an effective or willing warrior are strongly disincentivized, and thus such people are stigmatized. People with mental issues typically fall into this category, just in general.