Kartarpur Sahib is an extremely important matter not just for the Sikh community but others in north India who have great reverence for Guru Nanak his teachings. So one cannot overlook the importance of Kartarpur Sahib in bilateral relations. This corridor should have been done long time ago, there were various reasons it was not.
Remember that Jinnah soon after partition bought land in Bangalore in the hope that India-Pakistan relations would be along the same lines as the US and Canada. So while he was Governor General of Pakistan he could still hold new property which he had bought a few months before partition in Bangalore, in addition to his own house in Bombay, which is now known as Jinnah House and houses the Indian Council of Cultural Relations.
Unfortunately, Jinnah as well Liaqat Ali Khan who was the PM passed away soon, and in both cases there is some mystery about their deaths. The Pakistan Army, however, thinks that it is the protector of Pakistani sovereignty and identity, and India, and of late Afghanistan and Bangladesh, is the greatest threat.
So they use asymmetrical warfare to attack these countries. Civilian governments may want to improve relations with neighbouring countries, but foreign policy with neighbours, strategic policy and nuclear policy are all under the Army and ISI, and each time the political leadership tried to follow a different line they have come to grief. After suffering countless others, India has concluded that that there is no point in following the policy that terrorism and talks can go together. The US has also given Pakistan the same message. The only friends Pakistan really has are China and Saudi, and to an extent the UAE.
As for concerns that our Sikhs could get indoctrinated while on pilgrimage, our Sikhs know how Pakistan had persuaded Islamic countries not to allow Sikhs in their countries saying they are the worst enemies of the Muslims.
Gradually the Arab nations realised that Pakistan was lying. But the Sikhs also know that many of their places of worship are in Pakistan, so therefore they are not going openly against Pakistan fearing that their visits to these shrines would be blocked. But Sikhs from abroad are vulnerable because they are told by Pakistani and other anti-India forces that they can become a modern Israel.
In the 80s, I was there when some Pakistani students asked General Zia-ul Haq why Pakistan was supporting the Sikh community to go against India, when they are supposed to be enemies of the Pakistan? India is our enemy, so we have to use these enemies to work against other enemies, replied Zia. The Indian position thus has to be nuanced, protect the interests of the Sikhs in India, make sure that their shrines in Pakistan are well maintained, and they are allowed regular visits, the same way that Hindus would like to go to Mansarovar and Kailash in China. But this can’t be at the expense of our security.