I think it's not good behaviour from the top athletes since we have more and more "cocky" youngsters.
I played tennis and I can really understand them, like Caroline today, but when you are a big PRO than you should have in your mind that millions are watching you...it really looks ugly
Should they be punished when they decline to shake opponents and/or umpires hands?
No, it's an act of SPORTSMANSHIP, that's why footballers shake hands with their opponents before the match, volleyball players after the match, etc...
And that's all 'cause little kids look up to them. That's why nowadays we have so much kids playing tennis, yelling at umpires, calling their opponents "bitch, asshole..." and so one. Part of that they pick up from the house, but who can blame them when they see Top 10 player doing the same thing on TV