To what extent can the attack on Jewish money-lending be seen as a projection by a Christian culture, long ambivalent about charging money at interest, but now doing so, given it's necessity in an age that increasingly depended upon the investment of capital
I really don't have sufficient knowledge about the nature and extent of attack on Jewish money-lending by christian or any other group of people to, to justify making any comments on it. However in this case there are some general principles involved that have a bearing on these issues, and which point towards forces that shape the course of events. I would like to put forward my understanding of those general principles.
The concept of what is considered right and what is considered wrong in a society changes with time. These changes occur partly in response to changing requirement of different times. Let us tale the simple case of intellectual property rights. Today it is considered unethical and to violate anyone's intellectual property. This right is now defined by law in most of the countries today, and is protected by law. However a few centuries ago the concept of intellectual property did not exist. This concept was developed and introduced in modern societies as a means to encourage people to generate new knowledge.
The case of usury is also similar. There was a time when perhaps charging interest on money lent to others did more harm than good to society, and at that times it was right to condemn this practice. Today, charging and paying of interest serves many useful purpose like, directing surplus resources of individuals to productive activities conducted by large enterprises, and providing a means of income to old retired people.
In view of this we need to not take harsh view of a section of society for following a practice that their ancestors condemned many centuries ago. By the same logic, it might be right to tale a more understanding view of people practicing money lending business in earlier time. It is quite possible that they did serve some useful purpose though people who did not understand this continued to be prejudiced against it.