A more diverse SOF makeup would absolutely expand operational capability, IF all standards were met. I do think it is politically correct, but at the same time, that does not make it any less true. As far as the affirmative action part, those types of efforts can be detrimental. Holding one person back for the sake of another moving forward is prejudice no matter how you cut it. Just because you have "too many" Caucasians and want more African Americans does not make the changing of standards by a group less racist, just cause they are towards whites. It's a tricky topic that all parts of life are currently struggling with. We see it in colleges with scoring and acceptance. The school is saying they gain more by a greater diversity pool of backgrounds than they do from just having the best students. Is there merit to this? I don't know. At the individual level, it seems unfair. On a larger scale, I can see how the claim works. I can say, some of the most impressive SF guys I have served with were not your cookie-cutter style (6ft, 200lb athletic white dude), though 80% have been.
I think a bigger part is recruiting. The amount of minorities that try out is significantly lower than that of white guys. I've heard lots of reasons for this, but none of them do us any good. Recruiters need to do a better job of reaching their target demographics. It's tough to get more African Americans to Group when only five guys are going to SFAS and statistically four will fail (from all races).
Lastly, diversity is not just race. Its sex, age, background, ethnicity, religion, etc. We get too focused sometimes on just the race part. It needs to be much more than that. Not all need to be for the same job. I for one think there is a spot for women in SOF, it just might not be on a traditional ODA (or maybe it is). I think having a large pool of a diverse group of people gives commanders options for more situations hopefully leading to greater success for the US military in its endeavors.