A common misconception is that by secularising the country, religious extremist groups like TTP/ISKP will lose support, improving the security and economic situation of Pakistan.
The reality is, terrorism in Pakistan has no ideology; it is a result of genuine sentiments of vulnerable segments of society being exploited by malicious foreign actors to do their bidding (like destroying P3s and F-7s).
Removing Islam from Pakistan will not remove these sentiments, nor will such an undignified act of self hatred pacify the foreign hands behind the terrorists. (Rather, the world will laugh at you for surrendering your core ideology with such cowardice).
If Pakistan become secular, instead of facing a single religous terrorist group (TTP), the state would be fractured along the lines of its 60+ ethnicities, each with their own terrorist outfit. Imagine instead of just TTP, you have BLA, SRA on steroids?
As long as there is a largely illiterate and poor population constantly being exposed to hostile propaganda exemplified by genuine failures of governance, there will ALWAYS be a recruitment base for foreign controlled terrorist groups.
So what happens next?
The state would Balkanize along ethnic lines. Then the Indians would swoop in, dispose of their useful secular ethno-nationalist idiots, and embark on an Israel-style program of settler colonialism, just like they already are in the secularised occupied Kashmir valley. In the west, the militant Pashtuns and Baloch would be genocided Gaza-style and similarly replaced with Indian settler colonists. At best, the new ethnic states can hope to live as undignified slaves of India, like the Bangladeshis have for most of their history. (So much for the Sindhudeshis gaining freedom from UP-Bihari foreigners…)
There is no benefit to secularism - for Pakistan, it is as absurd an ideology as khwarji extremism is.
Instead, the state should strictly enforce moderate Islam, emphasizing the core principles of deen to ensure social harmony.