...A rose by any other name would smell as sweet..........Romeo and Juliet, Act I, Scene 2, W. Shakespeare.
By religion I mean Christianity, by Christianity I mean Protestantism, by Protestantism I mean the Church of England as established by law.... from Tom Jones, by Henry Fielding.
Imagine ... no religion............John Lennon.
Names are specifiers and classifiers, and, as in Shakespeare's play, sometimes an excuse to engage in mutual murder. That's pretty much the case for the Fielding quote as well, and Lennon is pretty explicit. A curious inversion of the Fielding character's sentiment has become a meme in some Hindu nationalist circles: the claim that Hinduism is not a religion.
The Indian Prime Minister:
“The Supreme Court in India has given a nice definition to Hindu dharam… The Supreme Court has said that Hindu dharam is not a religion but a way of life... I believe the SC’s definition shows the way,” Mr. Modi said.
Of course the other big religions like Christianity, Islam, Buddhism, Confucianism, etc. all prescribe a way of life too. Things get a bit uglier when one looks into the details of the context in which the Indian SC made its proclamation: a case in which Hindu temples wanted to preserve some explicit privileges despite the Indian Constitution's explicit prohibition of religious based discrimination.
Here is another advocate of the not a religion story.
Defining what is and is not a religion turns out to be just as hard for scholars as the above opinions suggest. Practically speaking, in the US it's important for tax purposes. I wonder how US Hinduism handles that - do they claim religious exemption?
I'm afraid I just fall back on the "looks like a duck, quacks like a duck" algorithm. Gods? Check. Temples? Check. Public and private rituals? Check. Elaborate body of superstitious nonsense? Check. Willingness to organize in mobs to murder outsiders or violators of tenets. Check! It looks like a duck to me.
There is also the fact that powerful elements of the "way of life" in question have clear cognates in the Indo-European religious systems that once dominated most of Europe and much of Asia, including details of social organization and names of deities.
Which brings me back to the only thing I can recall learning in one of my college philosophy classes: word definitions are ultimately conventional, and hence have an arbitrary element. So if you want to claim that something or other is or is not a religion, go ahead, and I will go ahead and try to decide if you are speaking the same language that I am.
UPDATE: Arun has a detailed discussion of the peculiar legal and societal circumstances that led the Indian Supreme Court to the seemingly paradoxical decision that Hinduism is not a religion. As well as I can summarize, it's a product of attempts to protect minority (Muslim, Christian, Parsi and Jewish) privileges enshrined in the Constitution. Minority rights tend to make things complicated.