After giving the commonality a lot of thought I could only name two things all Pakistanis that I know like:
Love of cricket and mangoes.
It may be on a lighter note but I do agree that there are too many differences of opinion, ethnic, religious as well as linguistic. But as on post has already mentioned is plurality a bad thing? IMO a multicultural and heterogeneous society is always a good; any society with no divergence of culture would be boring.