Addressing your points in order:
1) Racial paranoia exists across all given ethnic groups, and in most cases is distilled down to what they are really - honest mistakes.
2) This does happen, sure, but said innocent people are often found to be guilty of massive powerleveling and lolcow-worthy behaviour that wouldn't endear them to even members of their own race. Most consequences of these false positives would be attributed to the actions of perpetrators, not their racial identity.
3) PCness has always existed in one form or another. In actual polite societies this would be called
social decorum, i.e. responsibility of the individual member for respectful interaction.
4) This phenomenon is not just limited to whites and is more often than not precipitated by local economic decline via external/national factors. Demographic exodus is a result as other neighbouring locales gentrify and become respectable.
5)
This has been proven to be demonstrably false elsewhere on this forum.
Conclusion: Diversity is a flawed system and does not necessarily work in all cases, but like all policy has borne fruit elsewhere, like in the multicultural community policies of Australia and other places in the aftermath of the collapse of their white-dominant social policies.
Fortune 500: If you had bothered to look at the leadership stats for all five years that Apple is tracking (presumably where your argument is), you'll see that there has been no discernible change in those years with consistent 70% occupation. Also Apple does not stand as an absolute representation of the Fortune 500 - it is a nice piece of the pack, but it is not the whole pack.
Universities: Same deal, UCB is just one campus among thousands in the country. One campus the entire country does not make.
Demographic change: That's a statistical projection of demographic trends, not absolute truth of the future. Percentages are also deceiving - immigration is pushing the total number up and therefore conflating the percentages. The number of whites isn't decreasing, its lead is just narrowing as immigrants settle and populate.
I know I probably fucked up by even giving this reply but what the fuck. One should always fight fire with fire.