I don't think it's a no true scotsman thing, although as I was writing the comment I did worry that I was veering into that territory.
How one defines a Democrat varies, and only some ways of defining it make sense with the sort of Democrats you describe, and I don't think the overlap of "Democrats" and "people who identify with a specific political -ism" contains those. This will vary a bit depending on how one is interpreting "identify with a specific political -ism". I think this is where the disagreement lies.
I was thinking about the hazards of bad government, and wondering if there was a way for the LW community to do something to oppose them, and it occurred to me that we might be picking up the problem by the wrong end.
The usual way of thinking about political action is to start with one's political identity (progressive, libertarian, whatever), and that's likely to put one at odds with people who have opposed identities.
Instead, I believe there are projects which could appeal to rationalists across a wide range of the political spectrum. A couple I can think of are opposing the war on drugs and improving judicial systems. Any other suggestions?