New money in the form of credit must be "created out of thin air". Money is not necessarily tied to real wealth, although it should be made to conform to the reality, which means it should be made to reflect real wealth (i.e. goods and services and the capacity to produce and deliver these), but there is no implicit connection whatsoever. They want us to believe there is an implict connection, however.
So it is not the fact that new credit is "created out of thin air", it is that new credit is created out of proportion to real wealth, and it is created by banks who claim ownership of that credit, determine what costs may be charged for its creation and administration, and what laws will govern it. At present, we grant banks the right to create our credit for us, claim ownership of it, and charge excessively for their work.