Just keep thinning the herd until the stupid people are all gone. :D

At first blush their plan looks evil as hell. But if you're familiar with the results overpopulation is causing, it could be seen as the tough love we've been needing.

Normal flu deaths are just not doing the job, as there's tremendous lag inherent to a system that only takes people decades after they've bred.

The scoffers say any eugenics program by our lovely overlords would focus on the non-compliant, who naturally oppose their plans for us. But why not just take the easy and efficient route? Get rid of the most stupid and credulous elements in your gene pool, without having to go full gestapo and risk stampeding the herd. Like Jonestown on a larger scale, but the flavor-aid is injected, not swallowed.

Species management is not my forte, and I'm also not privy to their actual goals (leaks and documents notwithstanding), so there are probably a number of considerations I'm missing.

Anyway, anyone inclined to accept the injection of the substance after the show they put on should do so, with a hearty "Thank you for your sacrifice" as their reward. And maybe an ice cream, or a $100 bill.