Just because if something was, to use your words, “UNIVERSALLY understood for almost 2000 years”, does not assure me that humans with finite minds have been infallible in their understanding for all of that time. It takes faith to believe that just as it does for those today whose understanding of God’s word has grown and evolved over the course of time.
But your last sentence I don’t understand. Slavery is okay as long as the slaves are not limited to a single race?
It sounds as if you are nitpicking at things to boost your failing argument. Slavery is okay if it’s all races? Really? I can’t believe you would ask that.
You are trying to create a straw man argument to avoid the real issue.
Homosexuality is very clearly wrong in the bible. Please go back and re-read the quotes people kindly offered you. In fact, there are more quotes regarding the status of homosexuality than references to the trinity (the actual word “trinity” isn’t in the New Testament), yet, we don’t argue endlessly about that. Most Christians believe in the trinity, despite the word not actually appearing in the bible.
In addition, homosexuality is wrong because of how God describes marriage. He tells us that a “man’s seed” is for procreation. This cannot occur naturally except between a man and woman. It isn’t as much about saying “no, you can’t do that” as it is about understanding what sex is for and appreciating it as a gift from God. Their are limits to what ‘straight’ people should be doing as well because certain acts do not allow for procreation (use your imagination). Read Theology of the Body and then try to justify homosexual (or other) acts.
That being said, we are also told to love our neighbor, without any caveats. Anyone who injures, attacks, abuses or otherwise harasses someone because they are gay is clearly not loving them. The Catechism also tells us very clearly to treat everyone with respect and dignity (hey, there is your slavery answer, lol!). So, telling a gay person they are going to h— is neither loving them or treating them with respect and dignity. No one converts and invites God’s children by being abusive and mean. Pope Francis recently scolded priests who have dismissed gay people in the past. Jesus would never have dismissed anyone.
How should Catholics behave towards gay people? The proper attitude is love. Just love. I think it’s also only appropriate to explain the teaching if asked, and then, do it gently. If someone asks, then they want to know why. If you aren’t able to explain why, then refer them to someone else. If you can’t be charitable, then leave people alone. And never, ever assume anything because of the way someone dresses, speaks, or their mannerisms. If they don’t ask, you are likely to only hurt and drive them away by bringing it up. Remember, society tells us over and over again that many things are okay, such as abortion, divorce , and sex outside of marriage. All these things have good reasons to be wrong and should be approached gently when explaining why because people have been told the opposite all their lives. Even if you are certain a person is gay, you still have no idea whether or not the person is active in that lifestyle. So, love is the best approach for everyone and give them the benefit of the doubt. If they go up for the Eucharist, that’s between them, their confessor, and God, just as it is for divorced people.