It has nothing to do with Indian citizens? A law passed in India does not concern Indian citizens? I am not sure I can make sense of what you are saying.
If you are saying that the law does not affect current citizens, then, I want to say that It does not have to to justify the protests. Because the protests are about how it drags religion into how citizenship is granted.
It discriminates people based on religion.
That itself, without going into anymore details, is enough reason to protest against it.
Now, there are some arguments that say we already have different laws for different religion casts etc. But that argument is shallow, misguided at best, blatantly malicious at worst.
Because such things are there because the idea of being secular overrides even having consistent laws. Because it allows people to practice their religion.
In other cases, were certain reservations are provided to people of certain cast, they are merly to target a subset of population that was victim of a bad cast system in the past.
You can see that both of these ideas are very much in the spirit of secularism, and in first case, even overrides the need for consistent laws.
This bill shatters that very idea, like to its core.
In a set of people in which all members have same attributes, except for their religion, it makes it much easier for people from certain religion to obtain citizenship.
Now, one can argue that the religion filter, as we saw in the second case above, is meant to target people who were fleeing from religious persecution. But that argument also does not help here. Because then it only helps people who are fleeing from religious persecution from being a Hindu, and it does not help if you are fleeing from religious persecution from being a Muslim.
And why drag religious persecution into the whole thing anyway, people are made to suffer for various reasons in a lot of places, many of which does not have to do with religion.
No, this "religious persecution" thing is a very clever way to mask the actual intent behind this act. And in fact, this religious persecution clause is not even present in the actual law [1].
And people are calling it out en masse.