The Vivian Maier pic is a sneaky one though - interesting for the fact that the self-portrait is only a device. If she had pointed the camera directly their way, I suspect even then, people would be looking down the barrel - so to speak. It's still very easy to make candid pictures, even in crowded spaces. I think the real issue is that photographers are too self conscious when making pictures now, about being perceived as voyeurs. If you're haunted by that idea, you wouldn't have made a very good street photographer in the 1950s either. You have to be confident at ducking and diving and being a little brash to be a street photographer. If you have social anxiety disorder, pick another genre.
One of the classic stories in photography is told by Joel Meyerowitz (in his book Cape Light) about seeing Cartier-Bresson in New York, in amongst a parade, pirouetting and doing all sorts of cheeky things to get pictures, including throwing his camera at a mans face while keeping hold of the strap and catching it again, like a yo-yo. Maybe all you reluctant street photographers should start dancing classes and karate on the side?