Possible actions:
Tell him that Linux isn't all that. Add in that, just because Ubuntu is abandoning Gnome for Unity, doesn't mean that the Apocalypse has arrived.
If I have a weekend free, I might possibly see if any of the female cult members are hot. Given their predisposition for unthinking compliance, seducing one shouldn't be that difficult. Also, if it is a suicide cult, they won't be around long enough to cause issues later on.
If I have more than a weekend free and I don't feel like letting Darwin take place, I might possibly join with friend and then destroy the cult through public logic attacks on whichever glorious leader they were following. This is more amusing than just seducing one of the members and may still result in hot cult members giving me their "allegiance".
Just pull my friend out through the use of logic and long-standing friendship and let the rest burn.