The denigration of white players vs their black counterparts by the press seems to me more a factor of career-preserving cowardice rather than any conspiracy. This is worse for QB than any other position, since they get the most attention.
As a reporter or writer doing a piece on up an coming talent, you certainly have a handful of negatives to say about any player, white or black. The problem is that when you state the more obvious negatives about most black players they come off as being stereotypically racist. If time tells that you are correct, you gain very little, if you predict incorrectly, you lose greatly. With white players, it is the opposite. You don't lose anything by skepticism and negative reviews of a white prospect. If you are right about them being a bust, you gain credibility, if you are wrong, it's because the white player was a hardworking overachiever. It is acceptable in Western society to admit openly that you never expected a white person to have what it takes to succeed. To openly state the same thing about a melanin-blessed individual opens you up to being called a racist. Not everyone can pull off what Gruden does and simply be positive about every single player out there. You have to be brutal to SOMEONE, and career risk/reward says it's simply safer to unleash your reserve of scorn for whites.
The irony is that the real racism in all of this is the very attitude taken on to avoid being racist itself. If an "anti-racist" hears someone attacking the mental fortitude of Cam Newton his mind immediately goes straight to the notion that it must be because he is black. Why does he think this way as a color-blind anti-racist? Why must he overcompensate with illogical platitudes about a black players mental attributes first and foremost if not to make up for his subconscious feelings that he needs to help that player out in that regard?
These same career/face preserving attitudes on race and culture affect coaches and talent scouts just as much. A talent scout's career can survive missing out on the next Johnny Manziel because he is undersized or mentally immature/undisciplined. His career may not survive missing out on the next RG3 for the same reasons. A coach can survive benching an Alex Smith in favor of Kaepernick. His career may not survive the reverse.
When someone comes back with the old standby that "the best players play," what they should really be saying is that the players playing are the ones that have the highest odds of preserving the careers and social acceptability of coaches and talent scouts.