Get in there and push back against China Bad propaganda.
/r/UrbanHell is one of the better places to push leftist messages on reddit. It's big (600,000+ subscribers) but most comment sections are manageable, and housing conditions/urban development is so fucked up in much of the U.S. that you can find a pleasant amount of support for public housing efforts, even in AES states. "These big scary AES states actually give a shit about their people" is also a great way to get people to question how scary leftism actually is.
I also recall some good "the Korean War was actually genocidal slaughter" content on a few DPRK posts. People are a lot more receptive to learning stuff like that outside of explicitly political subs.