Because common sense says terrorist shouldn't have nuclear weapons. Just like how children shouldn't play with fire. Irresponsible as hell.
What's to stop Iran from nuclear blackmail? What's to stop Iran from giving a bomb or bomb material to one of their proxies? Or if one goes missing can't imagine their security protocols will be as professional as any real nuclear power state besides Pakistan who is equally on the same threat scale as Iran in my opinion given their terrorist elements, poor command structure, and support for terror.
I think American propaganda might be an issue here. What is a terrorist, and what is a valid government? What is the limit of homeland defense, is it invading and imposing law onto foreign lands which is good for a subset of people that is backed by a nuclear arsenal/military? I mean if we look at the history of the development of nuclear deterrence it creates more dialog than it destroys. You're not going to invade a nuclear country, you can do propaganda campaigns and hope the country collapses. I mean can we say the Cubans the united states trained were terrorists, can we say the pkk are terrorists? I mean terrorist is a term coined for a government (individual government entity) to make people afraid of a grouping of people.
If you look at the attacks by the Chechnians on the Russians... they were labeled terrorists because Russia pissed them off and they began to attack Russia. If we look at afgan terrorism the reason why they came here was because we pissed them off over there. It's not logical to think these groups weren't triggered by an action caused by an entity. Can the United States be considered a terrorist entity due to killing civilians in other countries? Where is the line of being a terrorist any attack will likely yield civ issues be it on an economic, military, or manufacturing base.
We are using words to define something that's convenient for us, yet we don't use it on things that aren't for us. The CIA fund terrorst operations, Mossad, and same for Saudi/Turkish/Russian/Iranian groupings. Even Korea (both north and south) somewhat funds terrorist operations.
Modern-day "terrorist groups" are just groups funded by a government in almost every aspect which are used to gain influence in a region and flip it.
IF we look at why these Middle Eastern terror groups got big it's because of the entrance of America and Russia into the region. The reason why afgan is ran by an ISIL origin group is not because of just threats we can look throughout world history where threatening groups still get overthrown (soviets, brits, congo groups, slavik groups, dynasties... and more). So, when more people support a group and defend it, the group maintains power. If most don't believe in the cause the group will fall out. Look at turkey riots/protests and how many are gathered. Look at how many people "Gathered together" after 9/11. Look at how many gathered together after the "border invasion" the Republicans claim.
You have to be more intropsective to the geopolitical whole and not just use a term coined to defend a notion fed to you by a grouping of individuals. The closest thing I can consider a terrorist attack would be the marathon bomber, the subway gassers, and some other situations. When a situation targets individuals directly. Not an economic sector, not a military base, none of that. The truck rammings are a terrorist attack, the beheadings in American culture can be considered a terrorist attack and I would consider it a terrorist attack; though, those people were likely captured because they had connections to intelligence agencies. It's very rare for a random person to get grabbed up by an intelligence network.
So who's truthful, is it something that's fed to you as a kid or what benefits you in the moment, or is the term coined across all different aspects even against your own government?