If they realize that we're doomed if we continue like we do currently, and that there are not any politicians that could save us, I don't know how to start talking to them about direct action, but if it fails and they're like "wHaT yOuR tAlKiNg aBoUt ViOlEnCE" I know I'd just answer them "oh yeah you're right we shouldn't do violence, violence is bad, we should definitely just let society litterally collapse instead of doing a bad thing", and then just admire how they're answering it

Either they have to come up with a third alternative or come back on how actually there might be politicians that could save us, (which usually is easier to disprove than the first situation you were in, depending on what argument they find), OR, they have to explain how actually yes, we should better let the society collapse than "doing something bad"