Well, calling it prostitution is the first issue as that is a patriarchal interpretation of what was taking place. The qadishtu were often the daughters of socially prominent and wealthy families since it was an honor to represent the Goddess in this way as her stand-in on earth.

"The sacred sexual customs of the female religion offer us another of the apparent ties between the worship of the Divine Ancestress as it was known in Sumer, Babylon, Anatolia, Greece, Carthage, Sicily, Cypress, and even in Canaan. Women who made love in the temples were known in their own language as “sacred women,” “the undefiled.” Their Akkadian name of qadishtu is literally translated as “sanctified women” or “holy women.”

Merlin Stone, When God Was a Woman p. 154

Actual prostitution was going on at the same time outside the temple but exchanging money for healing (which happens to take place via sexuality) is not the same thing. Read Riane Eisler's Sacred Pleasures book for more about how sexuality used to be a core element of spirituality until the patriarchs got ahold of things.