[The Professor]

This is apparently aimed at his personal views in the interview not his stewarding credentials. Stewards also run on a rota basis I think.

The very fact that Petrov and Hamilton have (publicly expressed) opposing views on the cause F1 has chosen to back is enough to bar Petrov from adjudicating on driver behaviour at an F1 race. Regardless of who's "side" you may be on with respect to the views on knee bending, shirts etc, the fact they disagree could affect desision making during the weekend. Like I said there are many other better qualified people they could employ.

Impartiality is the key factor here. If Petrovs opposing views do not affect his impartiality then fair enough. But better to take that element of doubt out of the equation.