The Torah indicates that they would be "vomited" out of the land for the way they lived their lives, which was considered an "abomination" before God. Did they believe the way that they lived their lives was disgusting? Was it only a cultural norm? Did they wake up in the morning and decide to be evil? We will never know, but for sure we can speculate that it was simply that their culture was not up to par with the God of Israel's standard of what was reckoned as "good."
When we as humans are born into the time period and culture chosen for us, are we able to know what is "good" and what is "evil" or do we merely adopt the standards of the culture in which we are born without a lot of thought? What God-given power do we have naturally and instinctively to determine right and wrong?
What if I had been born into a cannibal eating culture? Would I be wise enough to know that this is simply "wrong" or would I just be blind to it all and be chatting with others about how to fry human brains to maximize the nutritional value?
I am not so wise. I am only wise enough to know that my culture is a blindness to my eyes, and my only hope of having sight is by Divine Providence, and perhaps this willingness to keep my mind open.