Well a good captain and a sub-standard FO is not inherently
dangerous. The scary stuff is where you have an under-par
captain with a good FO (believe me I've seen it).
A FO is the Second In Command, and by that very definition
requires him to ensure that safety is not compromised. So it
means he has to know what the captain is thinking and query
anything he does that can be taken as a major deviation from
commonsense, airmanship, or SOP. If a satisfactory reply isn't
forthcoming it is a dangerous setup indeed.
I never mutinied during my FO days, but I came damn close
in more than one instance.