Speculation, is exactly that. Speculation.
Yes I think if we are honest we have all done it.
The down side is when a postmorten is carried out in the public arena. Pprune for example. These are read and in some cases reported by the media and believed by the vast majority of their readers.
In an accident, which involves fatalities, this can have a devastating effect on the bereaved, when some of the so call experts come up with a theory that could implicate the dead. Some speculation of recent events has been nothing short of slanderous, not to mention cowardly. Can the dead offer any defence?