When the Church relies on Scripture, then its attackers point to how things in Scripture that were once forbidden are no longer forbidden (e.g., consuming shellfish).  But Scripture was not created in a vacuum, and surely the evils of that which were deemed sinful were apparent when the scripture was recorded.  

Natural law has a way of expressing when we are acting beyond its boundaries.  For example, I think the AIDS crisis was a big red flag that natural law was being violated, and I would not be surprised that similar diseases plagued those who engaged in sodomy throughout history.  There are lots of clues that reveal how our bodies are intended to be used, but physical pleasure has proven to be an unreliable gauge.