Pakistan simply can not treat Afghans how Iran does, if we do it our own Pashtoon's will start blowing themselves in the Streets/Markets/School/s GHQ' in Pakistan. Pakistani Pashtoon's and their exposure to other ethnicities in Pakistan make them different than Afghan's, not by a large margin but they are still different. Afghans just can't live in Peace cause they always need a enemy, they will always use Islam as a tool of recruitment and unfortunately that door was opened by countries like Pakistan/USA/KSA/Israel all these countries radicalized them and the whole Warrior of Islam impression is now imprinted on their identity, not that I believe they are some Holy Warriors they are just bunch of criminals with lots of homo stuff and drugs.
Worse Part is that even if Afghanistan falls, it will horrible for Pakistan specially. Cause once again Pakistani Pashtoons will take millions in and many of them will turn against Pakistan in less than a generation, many new Terror Organizations will recruit them, and than in the name of " Islam ", " Pashtoon " nationalism more blood will be spilled. Afghans and by in Large Pashtoons or any Tribalistic society can not live in peace in this modern world. Look around the world, any nation where people are still using Tribal system or fighting over Tribal issues are either shit holes or war torn, including Pakistan. Baluchis another Tribal people who never get integrated with rest of Pakistan due to the nature of their Tribalistic societal structure.