Slate Star Codex, by Scott Alexander, is pretty clearly the most famous and public-friendly face of the rationalist movement at the moment.
- The Control Group Is Out Of Control on the weakness of a lot of modern scientific research and statistics.
- I Can Tolerate Anything Except The Outgroup on a general framework for thinking about tolerance vs prejudice.
- Toxoplasma of Rage on how the media works and why stupid topics keep coming up again and again.
- Meditations on Moloch, on the way efficient systems and ideas can grow and take over everything.
A lot of his thoughts come from the Less Wrong movement, best known for Harry Potter and the Methods of Rationality. You can google them if you want more content, but Scott puts a much nicer and more humane face on them.
One tumblr that defends rationalism but with an extremely compassionate and thoughtful face, that most of my dashboard at least respects greatly, is The Unit of Caring.
I don't know any particular post of her to recommend that summarizes her (which is "rationalism but nice about it"), but this is a good recent post about "how to be nice."
https://theunitofcaring.
And here is a post about prison reform from her https://theunitofcaring.