You should read the book "Sky Gods.". Pay special attention to the problems Pan Am had with captains who could do no wrong.
As to how many mistakes are ok, the answer is simple: as many as you can mitigate. I have yet to fly the perfect flight and I make mistakes. I catch most of them and the other pilot catches the few I miss. (the goal is to mitigate in the flight deck vs ATC or an incident!) This is why we stress effective CRM and pilot monitoring. Nobody is perfect and I highly doubt you bring an "A" game every time. Everyone needs to remember one thing when these things happens: There is always a chain of events that lead up to an incident. Multiple people have an opportunity to break a link and prevent an incident. So, that being said, if the pilots did not willfully violate policy or purposely act reckless, they should not be hung out alone to dry by armchair quarterbacks.
I hope there will be whole lots of mitigation as to why this happened, for those pilots sake.
To the it could happen to any of us line of thought? BS.
No, I have never had a perfect flight in 121 operations, because I'm always watching the other guy as much as what I do. I catch some of his stuff, he catches mine. We always do good enough.
But to say you PLANNED and BRIEFED and EXECUTED as two professional pilots who claim to be deserving a very high paycheck, and then land at the wrong field , with the excuse it could happen to any of us, is just BS on so many levels gentleman.
I'm all for waiting for the facts here, I hope they show many factors the crew faced, beyond the realm of normal, enough to result in a lack of some simple awareness of their true intended destination, I do., I really do.
Because, I am NOT going to tell the next paying passenger that "IT COULD HAPPEN TO ANY OF US!" If you really think that, please find other employment you are capable of doing to your level of competency.