I've settled on the word "progressive" as being the best general word for this.
The problem is that, outside of politics, "liberal" is the opposite of "conservative". "Add a liberal amount of mayonnaise," means "err on the side of too much", while "Add a conservative amount of mayonnaise," means "err on the side of too little".
But in politics, sometimes, "liberal" literally means "conservative". Especially in Europe, it is associated with free market capitalism. But in America, it is not generally associated with it.
On the other hand, the meaning of "progressive" is basically the same everywhere, political or otherwise, and it has a common-sense opposite meaning from conservative, unlike "left".