"Usury laws, in especial, which sometimes work great detriment to the business interests of whole communities, are in fact based upon the Bible conception that it is a crime to take interest for money loaned; although the common sense of mankind reject the notion in fact."
The free religionists were engaged in one of a series of attempts to reconstruct religion on rational grounds, specifically to "step beyond" Christianity. Abbot intended to plot "the way out of agnosticism" (as he titled one of his later works), but there seems to have been little agreement about the precise goals of the movement. Sometimes they sound like fairly conventional Christians, and at others they sound like fairly conventional atheists, though "theist" (without further clarification) seems to have been a favorite self-identification. Tucker would have known some of the free religionists through reform circles, and through William B. Greene (who seems to have been more radical in his rethinking of Christianity without anywhere near so much huffing and puffing), and others because New Bedford was something of a free religionist hotbed. Some of the figures associated with the movement, such as John Weiss and some of the other writers for The Radical, were individuals of considerable talent. When Tucker makes The Index the target of so many barbs in the early issues of Liberty, it is largely because those figures seem to have been replaced by lesser lights. In fact, despite the heat between Tucker and Abbot in this particular conversation, the pages of Tucker's Radical Review, published just a few years later, are full of Index regulars.
Tucker's letter sparked a debate that ran for most of 1873, and now you can read it in pdf form. It's fun to see a young Tucker stepping into deep water. It's also interesting to see other familiar names from the history of individualist anarchism surface here: Josiah Warren, Charles Thomas Fowler, Edwin C. Walker.
I hope to compile similar threads for other volumes of The Index, and am toying with the possibility of doing something similar with articles from Liberty. Let me know if this stuff is useful, as it is much more labor-intensive than many of the scanning projects.