That's really not true. For the last 60 years or so (basically since the civil rights movement) the conventional understanding of "freedom" on the educated American left has been significantly more nuanced. It is, after all, a nation with the institution of slavery enshrined in its constitution, so people tend to talk carefully about which freedoms they mean.

On the right, that never took hold (we probably don't want to get into why). So when someone says something like "freedom is a foundational ideal of America" they're effectively making a declaration of identity as an American conservative.

And coming back to the upthread point: if I hear that statement as "I'm a conservative!" in the context of "I'm an independent thinker!", then I'm going to be a little dubious about how independent that thought is when it's defined in terms of a political identity. Political orthodoxy is perhaps the SAFEST form of (to use the terminology from the article) conventional-minded thought.