Birkenstocks with socks is okay: http://www.gq.com/style/style-guy/shoes/200309/birkenstocks
Birkenstocks are a kind of footwear. Lots of people like them. What's the point of getting affronted by this? Does it make the world anything other than worse?
Understanding that people judge you by how you dress isn't snobbery, it's accepting reality.