> I've never been worried about my employer seeing my social media profiles. If I wouldn't do something in public, I wouldn't post it to social media.

Employers (and potential employers, for job applicants) don't use access to social media only to see what you post to social media and judge you by that, they can (and do) use it to see who you are connected to on social media, what they post about you, and what they post about other things, and judge you by that. They can also use it as a pretext to discern things that are protected by anti-discrimination law and which they would not ask you about directly for fear of lawsuits, as a means of difficult-to-detect unlawful discrimination, using, again, not only what you post, but information from others that is connected to your profile.

Now, you can limit your interaction in one of the prime mechanisms of social communication in modern society to mitigate the risks that poses (which itself undermines the point of legal protections, especially for things like religion and, in California, political affiliation), or you can, as many people do, create what essentially amounts to a bogus profile that simulates doing that which is shared with prospective employers, but neither of those are ideal.