I agree with your view about a penalty being too extreme, considering the level of competency of the two drivers involved.
But I have watched that squeeze replayed many times. After Vettel squeezed Button to the right, Vettel moved back to the left in order to enter the corner properly.
Hence even though I agree with you that a penalty is not called for, the squeeze was absolutely intentional, and Vettel's claim that he didn't see Button coming was a pure lie.
Of course Vettel moved over to cut off any attempt by the following car to get through on the inside of Turn 1. That is normal when you feel you have not had a good start. The point I think Vettel is making he didn't realise that Button was so close as he moved over.
Have you ever sat in an open wheeler and tried to see out of those tiny rear view mirrors? What impresses me most with those drivers is that they manage to see anything at all behind them!