This seems like an unwarranted assumption. Some people are going to want to keep others out, other people will have a different attitude. Why would you assume the incentives run the same way for everyone?

When the phenomenon locks out development in an entire municipality, we can stop discussing it as a benign consumer/resident preference, and start discussing it as the public policy problem it is. That's where we're at now.

In the US, I look at it this way: once you get your own school system, you surrender the moral authority to erect barriers to entry for new residents.

Because the outcomes all seem to be the same.

They don't, but empirically the overwhelming majority of people who are property owners in some area will either do nothing or actively oppose new housing being built in their area.