I disagree with this characterization. I live in SV and literally everyone I've talked to about privacy/anonymity on the internet sees the value in being able to partition one's life into different buckets for different audiences, and many of them actively maintain such partitions.
This has nothing to do with culture; this is about technology limitations and laziness. Companies like FB want to make it easier to track people online and tie everything you do to a single identity. They can certainly do a lot to link supposedly-unrelated personas through various forms of fingerprinting, but it's never perfect, and they'd love for things to be simpler.
There's also the issue of anon/pseudonymity: companies like FB don't like that because they want an indentifiable real-world person to be accountable for the things they do online.
(Really, think about it: the idea that the people who live in Silicon Valley have some magical weirdo culture where social and professional partitioning doesn't exist... well, that's absurd and doesn't even pass the smell test.)