Vettel's crash was down to misjudgement and error. I don't think he was being reckless. He tried to brake late (perhaps he had a little brain fade as well) and his car began to fishtail out of control. During this time, Button happened to be right in front of Vettel's (out of control car) and he collected Button.
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He lost control due to the sharp swerve.
the aftermath of the car, is very much important. No point giving a drive through to someone who is no longer racing. I have no doubt Vettle would not of been punished if he rejoined in 20th or retired.
It's also very important on why and how they lost control, in the first place. No one is going to get punished for a clipped wing running side by side though a corner, or misjudging speed difference with a back marker.
However you can argue a case, for someone following making a massive swerve losing control, taking out a championship contender whilst rejoining just outside the points in a perfectly healthy car. I think it is the sum of all of those which got him the penalty. Remove any one of those circumstances and he would not of been punished.