Curious: in your vision, what are negative externalities that you have in mind and how are they going to disappear with more dense living in the very same suburbs?
Environmental damage and the housing affordability crisis. I expect the first would be mitigated by increasing density in inner suburbs, thus creating shorter commutes with better transit options, leading to lower carbon emissions and slowing the spread of exurban sprawl (leaving more land for nature preserves and agriculture), and the second by increasing the housing supply.
But if you still hate this so much, you can live far enough from the city that it's not economical to build next door to you, or you can own enough land that it won't be an issue.
It appears that couple hours ago you did not count either as a negative externality, are you sure you are arguing in a good faith?
I'm not telling you that you can't live in the country if you prefer that lifestyle. I am saying that you shouldn't be able to dictate the level of density in your current neighborhood just because you are afraid of loud neighbors or you want to create artificial scarcity to inflate the value of your home.