Speculation
The problem with speculation is when it is in danger of becoming fact. Speculation is good as long as that is all it is... and it is made clear that that is all it is.
Speculation can be good when it is genuine discussion. As some have said here, it can lead one to think along channels where one wouldn't have gone had it not been for the speculation.
Some of the comments on this thread have made me think about how I do things - particularly with the comments on climb-out - and I will be changing the way I do things to reflect what I've learned here.
I was asked by officialdom to speculate on various aspects relating to an accident. I answered the queries as best I could from my own knowledge base. But, when my answers were read back to me, due to the way they'd been put into the written word, they were dangerously close to being stated as fact! I vigorously rejected that and made sure that it was understood that it was purely speculation - nothing more. No factual emphasis could be placed on it. I was particularly concerned that due to the way my replies had been phrased in writing, they could be interpreted as some kind of criticism of the unfortunate individual concerned.
That is a big problem with speculation. Speculation for itself is fine - as long as, as I've said, it is made clear that that is all it is, and that no criticism is implied.
As stated in a previous post - unless one was actually present, no-one can truly know what happened. However, the factual evidence uncovered in an investigation can lead to perhaps an informed guess.