A bunch of gangsters move into your neighborhood and start beating up everybody and stealing anything they can get their hands on. Some locals cut a deal with the gangsters. These greedy little shysters work for the alien Crime Lords and get rich. Naturally, such scum are shunned by the better class of their own people. But they don't like being shunned- more especially because knowledge of their degraded status reduces the commission they are able to charge the Mleccha Mafia.
So they claim to be far Holier and more Spiritual and more Moral than even the elite of their own Society. How do they get away with this imposture? Well, one way is by claiming to know the true interpretation of Holy Scripture- indeed, they go further and claim they know the true interpretation of any and every Holy Scripture that ever was or might come to be. Another way is to claim to be great patriots who only collaborated with the foreign gangsters so as to raise up the Nation till it once again occupy a wholly imaginary pinnacle of Purity and Enlightenment and true Humanitarianism.
Such was the origin of the Brahmo Samaj. Its founder thought worshiping idols was very very bad even though guys who weren't worshipping idols were self evidently no angels themselves.
Another thing which was very very bad was polytheism- like that of the Trinitarian Christians. Since conversion to Islam was no longer profitable this was an excellent argument to make. After all, Hindus who converted to Christianity were expected to lead a more, not less, moral life by their new Masters. That, by itself, disqualified converts from being the gangsters' compradors of choice. Hypocritical Hindu 'Brahmos' on the other hand were just what the Doctor ordered.
Unfortunately, though Brahmoism started off as anti-Hindu, its swift degeneration into an endogamous caste meant that Hindu values spontaneously regenerated within it and so, as time went on, even Brahmo's became patriots. Tagore himself stopped inveighing against the Freedom Fighters.
Why? He needed Marwari money.
Brahmoism had all but disappeared by the time I was born. Hegelian Marxism had been found to be a more potent source of mischief to the commonweal than even Benthamite Unitarianism. However, one wan hope remained- viz. the elderly expat Bengali Econ Professor. Don't write off Brahmoism till the very last of them bites the dirt pillow.