Why is homosexuality considered intrinsically disordered, meanwhile slavery is an evil that was allowed by God in the Old Testament as a compensation towards human weakness?

I'm a recent convert, having gone from agnosticism to belief in Christ in April. I had spent many years researching the scriptures and looking into Church teachings. The topic of slavery in the old testament had been circling around my mind for a while. I was told that the Old Testament is God preparing the Israelites for the coming of the Messiah. The ceremonial and civil laws were fulfilled in Christ's sacrifice, meanwhile the moral law still stands; This includes laws on sexual conduct. All of this makes sense, however, I have a hard time understanding why God was so outraged by homosexuality that it would rouse him to destroy an entire city, meanwhile He compensated the moral weakness of the Israelites by permitting slavery, albeit under specific rules. I am same-sex attracted and agree that homosexuality is outside of God's intended structure, but it is most certainly not as harmful as slavery.