There's land out on the periphery that hasn't yet been used for housing, but look: we urgently need to get our emissions under control because the course we're on will be catastrophic for the planet. Urban sprawl is massively inefficient.
Buying a house cannot entitle you to the neighborhood around you never changing if we are to have any hope of dealing with this mess. Change is part of life.
But I don't care what they want.
It's not up to them. It's illegitimate to tell a property owner that they can't build a duplex on their own property. It's an illegal taking. It's not up to a vote. My neighbor's opinion is irrelevant.
> There are plenty of places people for people to live and build.
Indeed, there are plenty of places to live and build and the burden is on those who don't want anyone to build near them to move to some place new if they don't like what their neighbors are doing. You have the burden exactly backwards. If you don't like what people are choosing to do on their own private property, then you can move. You shouldn't be allowed to tell everyone else to stop building.