Sterilize 50% instead
Barring a sudden shift in the ecosystem, I believe the balance of resources and consumption flow gradually, precluding any catastrophic outcome or sudden mass extinction. Nevertheless, Thanos could have just used the "stones" to render half the population infertile instead of erasing half of life. Free vasectomies, would have been a whacky plotline.
1. More humane / Less disruptive
2. Some might have actually preferred it but were uninsured / Reduced teen pregnancies
3. Less risk: Would take a while for people to catch on, maybe not even know it was him
4. Yes it would take 70 years for the effect, but that is a blip on the cosmic time scale.