Hughes,
the "ordinary person test" is not the same as a risk assessment in this case.
The risk assessment is to mitigate if not remove all the "risk" you can, this is a much different situation to had you not carried out the risk assessment.
For example:
a) An accident with no risk assessment: it could be said that you deliberately and knowingly did what you did without taking any precautions to prevent it... not so good, back to your safe argument and juries being pro safety.
b) An accident: Having carried out a risk assessment and taken all the precautions possible, or that you could think of makes it is easier to say that you couldn't have reasonably foreseen the occurrence.
A risk assessment is a "block" in the safety chain, James Reasons swiss cheese model, that acts as a buffer to the actions of the end user.
So when the duty lyncher claims that you knowingly endangered X, you can say, "not so! I did a risk assessment, carried out mitigating acts that I believed would stop X, this was an unforeseen occurance/act, possibly due to a "latent" error ...etc bang goes a juries/ judges beyond reasonable doubt....well that's the plan!"
Rule of thumb number 1. if you cant justify it before you do it, don't do it.
Rule of thumb number 2. if you can justify it think again considering that when we mess up in aviation we quite often kill people.