For most jobs, everyone who goes for interview is capable of doing that job, whatever level that job is - you just don't get invited in, unless your application form or CV demonstrates that you can do the job. You might have a written test or have to do a presentation as well, and again, once you've demonstrated that you can do that, and you've answered the interview questions, and all the questions are answered reasonably by all candidates, you are then left with subjective criteria - "do I like the look of him?" "I'm not sure she'd get on with Rachel - they're too alike", "would he fit in with the team?" "he comes across as a bit of a knob" "she's a bit of a miserable cow" "ooh, she's great, really wants the job, would work hard and throw herself into it". Very rarely is it so easy, that you can say "she didn't get that question right, so she's out" or "he did a presentation based on what he wanted to do, not what the brief was, so he's out."
I've interviewed people both in the private and the voluntary sector, adn while the latter had much more objective, buttoned down criteria on paper, in reality, choosing the candidate was every bit as subjective -because by the time you get to interview, the person who interviews you knows already, that you could do the job. It comes down to whether they want you in the office. And that is where the issue of "employing people who look like me" comes in and where positive discrimination could be very helpful to minority groups and women.