@Abbi …. Well there have been numerous times Iranian security forces tried to enter Pakistan and they were arrested by Pakistani security forces and were returned as a sign of good neighbourly gesture. Here a few links of 2009 and 2012,
BBC NEWS | Middle East | Pakistan holds Iran border guards and
Pakistan deports three Iranian border guards - DAWN.COM . However if Iranians want to test capability of Pakistan’s security apparatus, they are more than welcome, to try, as I said before we aren’t arabs, Pakistan’s military is a battle hardened force, which trains and has trained forces of several countries including your pilots in Shah era, who used to come to our airforce schools in 1960’s and 1970’s. And since you said more than half of the country isn’t under control of central govt, I would suggest try doing you research before writing useless rhetoric, I was born there, lived there for 20 years and visit Pakistan quite frequently so please do your research. As I said, the best way out of this situation is a joint operation and Pakistan numerous times in the past has cooperated including in the arrest of Rigi , these sunni extremists are a threat to both Iran and Pakistan, and should be dealt accordingly, but if you want to ruin your relations with a country with whom you share 900km of border just because of a bunch of terrorists, then be my guest !!!