He's far behind you when you apex, he hits you. He gets a penalty. Nice, isn't it?
In this case, Hamilton was already there. Massa had to cede the apex.
He wasn't at the apex though, he was over half a car length behind when they hit the braking zone.
It's simple geometry, to make the apex Massa has to turn in earlier than Hamilton. To get to the apex first Hamilton has to be far enough alongside so that the other driver has to concede the corner. Massa didn't have to concede the corner, he was ahead and he had the racing line.
Hamilton braked early, to back out. Just like at Singapore, he didn't back out quite enough. He caused the contact, but it was an error of judgement, there was no malice and he wasn't being overly aggressive like he was at Monaco. As others have said, this is the definition of a racing incident. Massa should not have been penalised.
That would make every single overtake into and out of a corner this season "dirty".
Yes, but there are different levels of dirty overtakes. There seems to be an accepted level of dirtyness; i.e. pushing the other driver offline is often necessary to overtake. We saw at Korea on lap 1 Button getting pushed wide 2 or 3 times at hairpins meaning he had to yield. But the low speed nature meant he could pull back onto the racing line after the other car has passed the apex.
At a corner like this you're not pushing them offline, you're pushing them off the circuit completely because it is high speed and there is a chicane with a patch of grass right after it. Alonso or Button (Infact, most drivers) would have thought better of this and would have backed out soon enough to avoid a collision.
I still believe that Massa's drive-through is not an indication that he was at fault, but more a consequence of the fact his car escaped the collision undamaged whereas Lewis lost 30+ seconds having to return to the pits to replace his front wing. Had it been the other way around, I'm 100% certain that Lewis would have got the penalty. Penalties should not be given on the basis of the consequences. Penalties should be given for who was at fault, regardless of the consequences for either driver. Massa was certainly not at fault. I don't think Lewis was either, he simply made a mistake.
EDIT: A distinction needs to be made between fault and mistake. For the purposes of my argument, mistake implies that it was accidental, whereas fault implies that the move was intended but the other driver didn't concede. Lewis did try to back out, he just misjudged the braking zone on the dirty line. He braked a good 10-20 metres earlier than Massa.