What is not at issue is whether Iran will invade anyone. No one expects that, at least not immediately. Rather, the harm of Iranian possession of nuclear weapons is that they will provide Iran with immunity from retaliation which will encourage it to escalate its Cold War against Saudi Arabia in the Gulf, and increase its assistance to Hezbollah and Hamas.  As noted above, Pakistan has in fact behaved in exactly this manner. Safe behind its nuclear shield, it has provided increasingly blatant backing to anti-Indian terrorist groups and opp is right to note that there is little that can be done about that. The best bet is not to allow Iran to do the same thing