@Sarkar bro simple example:
In a house A is earning 20000 Rs, B is earning 40000 Rs while C is jobless. GST says one India one tax like that if apply means A, B and C will get 20000 Rs each. Why a jobless C should avail equal benefits as others like B and A. What will A and B will do if they have their own family? Will they agree to divide income equally? Will you share your money with others....???
See I am using A, B and C instead of states. A,B and C's family represent each states problems. I don't want to create any partiality but I am just saying the fact.
Well bcoz of higher income of A and B they are already paying Income Tax as Direct Tax to Govt where as C does not need to pay Income tax.
Now regarding Indirect tax, all A, B and C are using Goods and services equally so all these Goods and services should be taxed equally as well. So as a Indirect Tax GST should also be same for all