• We have updated our Community Code of Conduct. Please read through the new rules for the forum that are an integral part of Paradox Interactive’s User Agreement.
Because it's the only way to join a game in progress?

Blocking a user instead of just denying the hot-join would work for trolls like the one you're describing, but seriously: just add a password if your game isn't open to the public. I for example, might try to join any non-password protected game that appears in the lobby without even checking the name of the game as soon as it appears in the list cause I don't care where I end up and just wanna play for a bit with some random species or another in some random universe or another. (aka the typical random hot-joiner who may as well just be a 'smart AI' for all the difference you'll notice from my presence xD)

When I get bored enuff anywho..