The decision for somebody to use their 5th Amendment right may have something to do with what that same professional may do with a misrepresented or misconstrued testimony believing themselves to be in the right. As I said before, would you want to end up the goat? Honestly, you may want this one to "get" them, and I understand people's reaction. But stating that somebody is unequivocally guilty because of pleading the 5th is pretty much an overstatement based on wishes. There are other reasons that somebody may invoke their 5th Amendment Rights.
I agree, there are other reasons Damo.
The first one that comes to mind, and the only circumstance I can see myself pleading the 5th in, is; fear of incriminating someone else. Someone whom you do not want to incriminate.
Otherwise? Personally, I feel if you plead the 5th, 9 times out of 10, if not 10 times out of 10, it's because you'd have to lie under oath if you didn't. In other words, majority of the times it's pleaded, it's because someone is worried about their own ass. A minority of times it's pleaded, it's because someone is worried about someone else's ass.
At no time, with a possible handful of exceptions that make the rule, is it pleaded for any other reason.