I think if 4 billion humans dropped dead next week, we'd all be better off long-term.
And you're dead wrong, even if all the cadavers mysteriously and magically turned into basic mineral components and were sprinkled all over the planet (instead of rotting wherever they dropped dead, contaminating air and water with diseases durably over the following weeks).
An 8 billion human population is overall better for mankind and also arguably for the planet, than just 1 billion.
Long-term, a forcibly reduced population would mean a lot less human capital (which is our true ultimate cap for progress potential), and a lot less competition for the same environmental resources, incentivizing a higher waste of these resources. Also, we'd be losing a lot of diversity, setting us back evolutionarily, and we'd just end up with more numerous but less adaptively fit individuals. This effect is well known and observed in all kinds of living organism populations, from bacteria to complex, social animals.
Oh and, if you'd honestly believe killing people is ultimately doing people a service, you'd have started killing already. Or are you just a cowardly homicidal hypocrite ?