The real solution is games designed for playing with friends and treat all non-friend players as potentially malicious.

Early first-person shooter games had this figured out (small servers with 20-30 regular players, the server admin could choose to ban you), RTS games have this figured out, many MMOs have this figured out (interact with non-friends sometimes, but they have to 'join your party', etc.)

Playing with random strangers on the internet who may want to grief/destroy your game, be incredibly toxic, or cheat against you in general.. that's the cost of playing with random people in a completely public forum.