You know I hear this said a lot and I kind of agree, but also disagree. My guess from just reading your posts here is that you are a thoughtful, self-reflective person and I just bet comparing yourself and the small mistake that you remember making sometime in your life and MR's behavior probably just doesn't compare. Just the fact that you have this much empathy, to me, implies a different way of being in the world than what I have seen evidenced by MR.
It is often said that you can't judge what you would do or what other parents do in these extreme situations. I agree to an extent--but I don't think that means that we can't take notice of things that are odd and I don't think it means that on a crime-sleuthing forum we can't ever assess those reactions and have those inform our opinion.
I was following a case where a mother of an abducted child, later found murdered, was out partying, shopping, doing shots, giggling on camera, etc etc. I do not think she was involved in her daughter's murder at all. She had been a meth ad dict and remained a meth addict. But I can certainly judge that behavior as wrong. It was not appropriate behavior and I know I would never act that way or any where near that way. A person can make those judgments, IMO. And it did make me suspicious of her for sure. That is the consequence of her choices. If you act weird, people will consider that in their judgments.
Many of us feel that MR is behaving strangely and that is our opinion.
You (general) can get into endless philosophical debates about there being no one truth or many truths (I know Derrida and the post-modern skepticism of truth) but even in light of those questions about absolute truth, we all still just do our best to come to some kind of approximation of truth with the information we have. I think that even in extreme situations there are still "wrong" ways to behave. Those behaviors could be explained by other things beside guilt (drug use, mental illness, non-adaptive behavior, trauma etc). some things are easily forgiven--others less so. JMO I do not think it is immoral or unethical to assess the reactions of parents when their child goes missing. JMO