Earlier quoted context omitted.
The notion that because a road was paid for with "public money", that ought to guarantee unfettered access to that road is just a fundamentally juvenile, silly idea.
I didn't say unfettered access, I said access. Unless there are specific, justifiable reasons, public things should be publicly accessible. i.e. you can't rifle through your mayors paper's or freely walk in prison, though many are sickeningly privately owned. You should, however, be able to use a public park. Would it be wrong to limit the use of a park to only the people within a block of it? Look, my street is used…
Wanting to minimize traffic on a residential side street for the privacy and safety of its residents is a specific, justifiable reason for putting up a "No through traffic" sign. You might not like it but it meets your criteria.
The funny thing is, whether you're talking about speed bumps or Berkeley street dividers when talking about "traffic calming measures," a simple sign (and possible but unlikely consequences for not heeding the sign) might often be an infinitely more user friendly option for both the residents and the would-be shortcutters. Turning onto a street and discovering speed bumps or barriers sucks, and they suck even more if you have to live there.
I lived in Berkeley and the sign strikes me as a gentle first step to take before altering the streets. On the other hand, I'm really, really doubtful one solution or the other is going to be universally more effective. I don't think the "no through traffic" signs one sees where I live now would have worked in Berkeley, for example, even though they seem effective enough here. Different crowd, different traffic patterns.