Prostitution was legal and regulated by the catholic church as necessary and understandable evil for centuries, until 15th century. Even Thomas Aquinas (huge stickler) agreed. And why wouldn't it be? It was what common sense would tell you. Learned christians would understand sexual sins are far from the worst ones.

Also additional context, before the 12th century priests were allowed to marry and have children. It was taken away, to consolidate the church's property.