This isn't as simple as speculation versus not. Isn't it just about maintaining a normal level of human decorum in discussing fatal accidents? For example, based on the husband-wife incident referred to in one of the underlying threads, I could observe fairly accurately that a diver who becomes incapacitated underwater pretty much has one chance at life, and that is if he is brought safely to the surface by his buddy.
Now if I continue on and "speculate" that this diver would have lived had his wife brought him up, I have assumed a bunch of facts that may or may not be true. And if I further criticize his wife for not bringing him up, I have built on my speculation and now I have leveled my criticism at a presumably grieving widow who may or may not deserve it, but of course I have no idea what happened there underwater. Which is where I think I would start to implicate the concerns of those who caution against "speculation." Some people will go down those roads, others won't.
But I might elect to use a scenario like this to explain to a group of students the importance of rescue training and reliance on a dive partner. And if so I think we could be learning from the situation. Frankly I am not sure that "lesson" would be different if it ultimately turns out the man died underwater from a massive heart attack, or that his wife tried but couldn't "rescue" him because he was panicking, or any number of explanations.