Without interest, inflation would be over the roof and could never be controlled especially if its from the demand side.
Our former finance minister Shabbar Zaidi gave a very good response to this dumb concept that you cant associate a banking system to a religion. And even if you want to implement this absurd thing, go ahead try it. Do further damage to the country, at the end, you will still take a uturn back to the proper banking system.
Anyone with knowledge on basic economics knows how important interest rates are
But Pakistan can always refuse to take loans ... i.e if they were truly a real theocratic country. Looks like the rulers don't believe in going by the letter of the religious doctrine that they have sold to the masses.