What would you have done if in Contador's shoes?
Same thing Contador did...Schleck did not have a "mechanical" breakdown. He mis-shifted going uphill, his chain fell off, he put it back on, and then it fell off for the second time. This is rider 'error' not a mechanical breakdown. The whole thing lasted 20 seconds according to Velonews.
Furthermore, Andy Schleck should not b*tch too much because when Contador rode with broken spokes and an untrue wheel during the pave/cobble section, nobody slowed down for him. In fact, it was this stage where Andy S. gained lots of time and basically got back into the real competition. During that stage, Chavanel had the yellow jersey and he flatted (once, maybe even twice) and nobody (let alone Andy) waited for him.
Also, during the now famous 'crashing stage' when Cancellera (wearing yellow) slowed down the entire peloton, the rider who benefitted most from this move, who otherwise could have kissed the T de F goodbye as he was many minutes behind the leaders...yes, you guessed it, Andy Schleck.
Everybody is picking on Contadior, but Contador had to match Sanchez and Menchov (currently #3, #4) who took off from Schleck and they also didn't feel that slowing down was indicated.
Finally, the vast majority of racers (including J Bruyneel from Radio Shack) support Contador's move.
This is a professional bike race, not a no-drop Sunday ride.