OK my honest opinion:
I think criticizing Iran or KSA or any other country should be allowed.. but if someone brings the sect into this.. that should be considered crossing a red line..
Shias aren't anti national.. brelvis/ deobandis and other sects too.. they aren't anti national.. But there are organizations in every sect that work against national interests..
TTP was one such example.. when they started killing, they didn't distinguish between a Sunni, a Wahabbi, a Shia or a Non Muslim.. Sipah Muhammad is another such organization that has been involved in terrorism inside Pakistan..
Because of Sipah Muhammad or TTP, we can't call all Shias or Deobandis as anti nationals.
But TTP was supported by Afghanistan and India.. and there are certain terrorist organizations that get support from Iran too.. Criticizing Afghanistan, India and Iran should be allowed.. but criticizing Shias of Pakistan because of Iran, Sunnis because of TTP and Hindus of Pakistan because of India shouldn't be allowed on PDF.