There is a theory by bell hooks that one way many immigrants try to assimilate into white America is often by buying into the racism against African Americans. Joan Walsh concurs in her April 22 Salon.com column: 'Embracing racism and xenophobia, sadly, could be a shortcut to white status for previously non-white European immigrants.' This is not an argument against immigration but a testimony that racism is a problem for the entire society and not just for the targeted groups, calling for all to be committed against racism in all its manifestations.
This is the original hypothesis: There is a relationship between x and y. Scientific minds will proceed cautiously by testing the null hypothesis: there is no relationship between x and y. If we find significant evidence to affirm the null hypothesis, then we will reject the original hypothesis. If we reject the null hypothesis, then we will affirm the original.
Let x be racism and y be terrorism. The news reporters overwhelmingly suggest that the x is religious extremism. Let us assume that they are right. Then let us ask if religious extremists tend to be anti-racist or virulently racist? That is a tendency, mind you; we cannot condemn all religious extremists as racist nor can we conclude that all racists tend to be religious extremists.
It may be argued that if they wanted to target fast-running Africans, they would have detonated their bombs one hour earlier. The brothers were apparently lone wolves who did not have a time-keeper to ensure that they targeted the winners alone. They had six more bombs with them in the police car chase but only two were successfully detonated. So their timing was off by 2 hours from the winners, but that is no proof that they did not have a racist grudge against Africans, perhaps for dominating their chosen sports. Yes, even some of those who come last in the race will be Africans (as the video of the first blast showed a black man running past) but it is no secret that the marathon is an event with disproportionate African participation.
The original hypothesis of a link between x and y may be a stretch but when you are born and raised in a country where the President calls Africans cannibals and where African students complain that monkey noises are so common that they no longer bother to report them, it is not such a huge stretch to hypothesize that young people socialized into white supremacy in such a society will tend to be racist.
Terrorism is a hate crime, so the hypothesized link between x and y appears logical. It was not too long ago that religious extremists rounded up black skinned citizens in Libya and executed them in front of video cameras. Religious extremists may try to convert non-believers to their faith but they cannot convert blackness to whiteness - hence the will to the final solution.
My suggestion is that we should not ignore possible racist motives (among other motives) because the disease of racism will spread and affect everyone. The bombers may have targeted black people but the whole society is paying the price. Racism-sexism-classism are challenges to all.