First, I know what most of you are going to say. I myself was an internet atheist 20 years ago, quoting Dawkins and Sagan at magic-sky-daddy believers. But this isn't about convincing anyone to believe.
This is about pragmatics. And, pragmatically, the single biggest enemy right now is the conservative Christian right. Anything to fracture that coalition benefits the left.
Luckily, their gospels are pretty left-wing. So, I offer for your consideration, the Christian angle.
I encourage those of you who went to Sunday school to brush up on your Scripture. Matthew is a treasure trove. When you're talking to someone on the right, start hitting them with chapter and verse.
If nothing else, this is initially shocking. They're supposed to be the Christians, and you're some filthy commie reminding them that Jesus called the wealthy priests hypocrites, and told us to feed the hungry and aid the sick.
They have defense mechanisms against your crybaby commie talk. They don't have defense mechanisms against their own scripture. At worst, you shake them loose from their script and confuse them, giving you openings for gentle deprogramming.
At best, they might reflect on their leadership and how closely they follow Jesus' commands. Anyone who really believes in him and really reads the gospels is going to wind up a leftist, whether they call it that or not.
Just food for thought. Read up on what Jesus said, use that against the people who claim to follow him. You don't have to believe yourself to recognize a powerful rhetorical tool.
If you say homosexuality is sin, you are basically renouncing Jesus.
They died a super painful death largely because in their opinion, nothing you do with a pure heart – that is, meaning to do good to others and having done your homework to try to understand if it is an okay thing to do or not – is sin.
They were tortured to death very largely because they said that whatever is defined as sin by the old testament is no longer automatically a sin. Jesus of Nazareth invalidated the whole list of sin definitions in old testament.
If you're basing your argument on the Old Testament saying something is a sin, you are renouncing Jesus, and therefore, you are not Christian.
I don't really understand why people want to be Christians in the first place. But, if they want to be, maybe they at least should care about what Jesus said according to the Bible and not just assume that Jesus was some idiot you can safely ignore if you feel like someone being different is automatically a danger to you. Something like 95 % or 99 % of people calling themselves Christians by religion are in practical terms renouncing the word of Jesus. Like, do they not know where the word "Christianity" even comes from?
Mrmph. That's what I say. Mrmph.