In other words, the core of the contradiction between India and Pakistan is religious contradiction.
India Pakistan devide was based on religion. This is a well documented historical fact. However this devide was only one sided. India never declare itself a Hindu state. We were secular before 1947 and after.
India is a land of multiple religions but when one religion starts behaving like superior to others, intolerant to others, demand special treatment, does violence towards others, its when problems emerge.
Core of ideology that drives Pakistan is return of Mugal era, islamic rule over entire subcontinent. This thinking keeps the devide wide open.
If Pakistan is willing to join India but keep Islam, will India agree?
India already has a muslim population bigger than Pakistan. India is not a Hindu country. Indian gov can't say to change religion of our own population how can they say it to Pakistanis.
In an unlikely hypothetical scenario, If Pakis ever want to join India. If such serious proposal is offered, Indians will happily accept such proposal as it removes a permanent nuclear threat and all terrorist activities.
So to answer your question in one word, Yes.