You've raised an interesting political-economy argument, though economists would debate several parts of it.

Your core thesis seems to be:

1. Healthcare is a major economic growth engine.
   • Healthcare employs large numbers of people directly and indirectly.
   • Aging populations typically consume more healthcare services, creating demand, jobs, research, and investment.
   • Medical innovation often spills over into other sectors through biotechnology, pharmaceuticals, diagnostics, information systems, and advanced manufacturing.
2. A eugenic policy aimed at eliminating elderly or disabled people could destroy a significant source of economic activity.
   • Beyond the moral catastrophe, it would reduce employment and investment within healthcare and care-support industries.
   • It would also remove accumulated human capital, experience, caregiving roles, and consumer spending from affected populations.
   • Many disabled and older people contribute economically, socially, culturally, and through unpaid labor that conventional GDP statistics often understate.
3. If demand collapses, governments may seek alternative sources of spending.
   • Historically, some governments have relied on military expenditure to stimulate industry and employment during periods of economic weakness.
   • This is often referred to as "military Keynesianism," the idea that defense spending can increase aggregate demand.
4. You argue military spending is a weaker growth engine than healthcare spending.
   • There is a longstanding debate on this.
   • Critics argue weapons systems produce limited civilian benefits compared with investments in health, education, transportation, housing, or public infrastructure.
   • Supporters counter that defense spending can generate technological innovation, industrial capacity, and employment.
   • The economic multiplier varies considerably depending on the type of spending and the structure of the economy.
5. A highly militarized economy can create political incentives for conflict.
   • Some political economists have argued that states with large military-industrial sectors may face pressures to justify or maintain high defense spending.
   • However, the claim that militarization inevitably leads to wars of aggression is much stronger and more controversial. History provides examples both supporting and contradicting that proposition.

One way to sharpen your argument would be:

"Eugenic elimination is economically self-defeating because it destroys part of the demand base and productive ecosystem of healthcare and care services. Replacing that demand with military expenditure may sustain some employment, but it redirects resources toward outputs that generally provide fewer direct improvements to human welfare and civilian productive capacity. The result can be an economy increasingly dependent on militarization rather than human development."

The strongest part of your argument, in my view, is not that healthcare spending automatically creates more GDP than military spending, but that treating elderly and disabled people as economic burdens overlooks their role as participants in complex economic systems. Modern economies are often strengthened by maintaining and improving human health, not by reducing the number of people who require care.