See that is where you Iranians are dead wrong, if you follow up project Chahbhar, Kulbhoshan Yadev activities and Uzair baloch JIT and information which was leaked by media , he was spying for Iran, Killing for Iran, and so on. Iran give RAW agents a project literally next to highly contested Balochistan where Indian interference is not a secret, they openly talk about it. Now tell me as a good neighbor as you say you are, why you let Indians into this project when they are openly bragging about supporting BLA and BRA ? Don't tell me that your Govt was such innocent chaps that they did not even expect Indians to send Spies disguised as business men or workers in Chahbhar ?
Again, Pakistan is not divided on any Sectarians lines, Pakistan is majority Sunni hence Shia's are in minority, there is no division among them as they live together for many years, clashes happen when someone from Sunni side or Shia side cross the line, we have Sunni's who claim Shia kaffir and incite hate, on the other side we have Prominent Shia scholars openly insulting Sahabah, Wife of Prophet SAW. The reason why Shia killing gets more attention is because they are minority, Pakistan lost around 80K people in this war, and majority of them were Sunni's and yet when you talk to Shia's in Pakistan they will claim a systematic killing or Genocide, why ? because their orders comes from Tehran, how do i know this? your Sect works in similar way and your clergy has a hierarchy, Whatever Ayatuallah says Goes .
Your Sunni Population also have their sum of troubles, and so please don't play saints here, lets be real and adults. Iran we all know has spread its proxies in every country where Shia are in either minority or majority, from Pakistan to Afghanistan, from Syria to Yemen. Yes Pakistan did the same in Afghanistan, but we did it because of USSR, we can not allow USSR who was in bed with India to be on our western side while India is looking at us aggressively from East, USSR must be defeated in Afghanistan, hence we have to take such drastic actions like supporting Taliban, second US did try to do the same thing with Pakistan, India on east, America and NATO of west, pushing their proxies such as TTP , BLA , BRA , JuA inside Pakistan to keep it destabilize, now America is leaving and Taliban sooner or later will over power NA, this is not something Pakistan has to even support Taliban with, they are strong enough to take NA down with their warlords, you know why? because General Afghan public hate these Child rapists Warlords, and the alternate given to them was Taliban twisted Sunni Islamic state, for the Afghans it was either brutal child rapists NA warlords or Strictly fundamentalists Islamists, hence they pick Taliban over them.
Now if Iran was sincere with Pakistan, it would never allow Indians close to Balochistan, second would never supported Terrorists Organizations like Liwa Zainabyon or support Target killings, they didn't and hence people who are majority Sunni in Pakistan will have no choice but to see Shia Iran as suspicious.