So yes, you're up against a student of the subject.
Here's my 8,000 words on Constantine; amongst other things he ordered that prisoners should get some daylight every day.
https://www.academia.edu/28971...
In the 19th century Christians not only led the moves towards the abolition of slavery - though, yes, there were Christians on the other side - they also pushed for factory safety legislation and child labour laws
https://en.wikipedia.org/wiki/...
Additionally the civil rights movement in the early sixties was led by and organised by Christians - both black and white; 'Dr Martin Luther King’s March on Washington was literally planned from the Methodist national headquarters'
https://www.theguardian.com/us...
Yes, you're right that in recent years that the visible and noisy part of the church, the Evangelicals, have largely become aligned with the Republicans. But there are many that aren't and are campaigning against the Trump migrant crack down; unfortunately those associated with Trump are getting all the publicity.
For a detailed discussion of the matter, agnostic Tom Holland's 'Dominion' provides a full history of the role of the church in moral change; over the centuries it has been extremely positive.