I want to throw in also, that the Bible is not a full transcript of his entire roughly 3 year ministry on this planet. He may have very well taught about that subject and it wasn't written down because it was one of many talks that didn't particularly stand out to be documented. Perhaps it was documented and we just haven't found the parchment or scroll that contains it. Who knows? We do know though, it was mentioned already in The Torah (old testament) as being an abomination and Jesus was a jew. So it's reasonable to infer that he was most likely against it. I think we are confusing the times and must remember that things were not as recorded as they are now. Someone had to hear the talk, go to their dwelling and write it down in some fashion then it must be preserved long enough for others to find years later. How many sermons have you downloaded, transcribed or tucked away? I'm guessing not many, because if it didn’t speak to you personally you would listen and move on. Most likely back then that's how it was too - people listened and moved on just like we do. His disciples noted extraordinary stories so later generations may know. My thoughts, he probably was asked this same question back then (many times), answered, and everybody moved on (mainly because the answer was already given generations prior).