Well that is initially what he got, a 30 second time penalty and was relegated to 115th place.
Then they deemed that not harsh enough because he endangered other riders. Whatever the case he did elbow him and in my book that is very unsportsmanlike and as it is a non contact sport then I guess he got what he deserved.
He did not elbow Cavendish, he actually never hit Cavendish with his elbow (only looks like that from some angles).
No but he obviously did it on purpose. If I pretended to throw an elbow at someone they are obviously going to flinch. You simply can't do things like that in a non contact sport.
Also if you get pushed toward the edge by another rider, you might use the elbow for balance ?
Also Cavendish didn't have to try to get through, so in some sense Cavendish pushed himself into the situation where he crashed.