pitching upzoning to homeowners

Higher property values? Not the way it works.

Yes it is. When it's legal to use your property in more productive ways, that increases the value of the property. Apartment developers are willing to pay a lot for land with single family homes on it, if they can build apartments there!

And what happens to the surrounding neighborhoods once people move into those apartments?

If this deal is so great, why do you have to propagandize for it?

The surrounding neighborhoods also become more valuable! Why would the presence of other people do anything else?

Weird question--why does anyone propagandize anything? Not everyone shares my view, just like people disagree on many others. Some people don't like change, they don't like immigrants, they don't like integrated communities. They want to live in exclusionary neighborhoods that override their neighbors' property rights, no matter the cost. I think they are wrong, and memes are one of the tools I'm deploying to defeat them.

"Why would the presence of other people do anything else?"

Well that depends how those people behave, doesn't it?

"they don't like integrated communities."

You mean they don't like higher crime rates that inevitably follow "diversity"?