Why is it so important to hire professional translators/interpreters?

The whole world must have heard/read the news about the recent Hillary Clinton incident in Congo. I am not too concerned with her reaction, but with another issue: well, apparently the interpreter made a mistake and misunderstood a student's question to the US Secretary of State. According to CNN, the student wanted to ask President Obama's and the Secretary Clinton's opinion/position, but the interpreter got it wrong.
I have seen the video (where you can hear the interpreter's voice/translation), but unfortunately the student itself is not heard, so it is still unclear who's fault is it.

My point is, it is important to always hire professionals, specially in situations like this, in order to avoid this sort of embarrassing moments. Now, I have no information on this person's professional background, but it seems to me she was just a little too confused. I mean I was confused just hearing her! I'm not sure the person hired for this job is a professional interpreter, though.

I am going to use a question from a previous post , "Would you approve of a medical student performing minor operations to pay their way through medical school? (Would you describe your brochure/letter/annual report/speech as "minor"?)". My guess is you wouldn't!

You can check the video from the incident here: