Landlords, yes, but also people who think that new market rate housing will destroy the character of their neighborhoods, or something.

Take it with a grain of salt because it's reason.com, but this video does do a good job of conveying a sense of how ridiculous the situation has gotten:

https://www.youtube.com/watch?v=ExgxwKnH8y4

Just off the top of my head for only the mission:

calle24sf for the mission:

https://www.calle24sf.org/en/

United to Save the mission:

https://www.facebook.com/SaveTheMission/

Anyone concerned about the impact on the environment in and around the city / increase in traffic / strain on limited water resources / etc.