The attenuated polio vaccine has already worked this way for more than 70 years. People can catch the vaccine like how they can catch the virus. This has had positive effects on boosting immunity in developing countries where the parents may be unable to take their children to be vaccinated, due to work commitments, expenses of travelling to the nearest clinic, etc.

Eventually we'll be able (as in it will be possible) to pinpoint some "contrarian" gene, then make something that only kills these individuals, and put it into mosquitoes.

Now if it's possible to do then obviously some government somewhere will do it (eventually), and no one will notice anything, say it's something that gives you a heart attack, and say we see a spike in heart attacks in 2050, it won't even be that significant since contrarian individuals are few, and just like that after a year the population will be a lot more docile.

It's still a sci-fi scenario now but it's scary to think about what the future will hold.