The U.S. invaded Iraq (wrongly, but let's look at it from their POV) fully knowing that a lot of their soldiers will die, but they deemed the invasion necessary for their cause so they were willing to risk the lives of a good number of soldiers in order to achieve what they wanted to achieve.
Similarly, the PCB thinks (again, we have to look at it from their POV) that it is necessary to host the final in Lahore because a lot of good can potentially come out of it, and it can help bring international cricket back to the country. They know the risks but they have faith that the Presidential level security will ensure that there is no act of terrorism. The safety of the foreign players is obviously of paramount importance, unlike the safety of the security personnel who will be doing their job. Similarly, the safety of the Zimbabwean players was more important than the safety of the police officers who lost their lives during a botched suicide attack outside the Gaddafi Stadium during the second ODI.
If we go by this logic, then no war is justified because it puts the lives of soldiers at risk for political and economic gain, and putting their lives at risk is not justifiable. However, this is not how the world works, otherwise the security personnel in Pakistan would have refused to provide security for the PSL final because it is not worth their lives, but that is now how it is. They understand that it is their duty and their lives are less important than the lives of the foreign players in this case.
The second example is illogical because a) it means certain 100% death b) there is no possible gain. I have absolutely no chance of surviving if I crash a Ferrari into a brick-wall at 200 mph, and I have absolutely nothing to gain from it even if I somehow survive because of a miracle, so this is pure suicide. On the other hand, the chances of a terrorist attack during the final are far, far lower than the chances of getting killed in the aforementioned example, and plenty of good can come out of it everything goes smoothly according to plan.