why does dante place usurers blasphemers and sodomites together in Dante's Inferno?

Both usury and sodomy are held to be "against nature" by which is meant that they sin against the very order of being. But why is this so? If we think of Capitalism and its expression in cultural liberalism we can see something of a reason for this. Capitalism is not per se the market or even business, it has to do with capital. What is capital? it is when the value of money is abstracted from money and made self-fructifying. That is, it becomes self-referential; it becomes oriented to itself; it becomes an expression of the logic of the same. Philosophers such as Aristotle and later Christian theologians, as have many economic theorists, argued that the vale of money is its sign in a system of barter. That is the value of money is derivative of a product of some sort. However, with usury, with lending money at an interest, money becomes divorced from anything other to itself. It is no longer first and foremost a symbol or sign of something other, a car, or house, or gold, for example, its value becomes self-referential. It falls under the logic of the same. Sodomites, or what we might call those who indulge in (male) homosexual and anal sex exhibit a similar logic. The natural order of sex is to be between a man and a woman, between sexual others (hence the term hetero-sexual, where hetero means other ) and it is to be oriented towards the production of new and other life. But in sodomy the logic is of a desire for the same. It is perhaps no coincidence that although sodomy has been around since the year dot (and of course not just between gay men, after all sodomy is rife in prisons and it would be a stretch to say that all the men there are gay), only it is only under cultural liberalism which is the expression of Capitalism that sodomy has become a celebrated cause and avidly promoted, just as usury is fundamental to a Capitalist economy. As for blasphemy, I am not sure as to its association here. One might speculate that if one has fully succumbed to the logic of the same then one might well grow in hatred towards the source of all otherness, namely God who is other to all creation having created everything from nothing.

Usurers

Easy. The Blasphemers were violent against God, the sodomites were violent against nature and the usurers were violent against order.

Because he had read Revelation chapter 21 verse 8.

I guess you don't know the Bible. There are eight classes of people doomed to eternal torment. They are listed right there. Read it and shudder.

It was his way to say "f*ck those Shylocks!!"