[anton]

Why would we not assume that the flight attendant called the pilot out, entered the cockpit and killed the other co-pilot and crashed the plane?

[Hot Tabasco]

Why would we not assume

There's also the possibility that the co-pilot may have simply passed out due to an unreported medical condition........

[Sicon]

Why would we not assume that the flight attendant called the pilot out, entered the cockpit and killed the other co-pilot and crashed the plane?

Uh, because it is considerably less plausible and less likely than what they are currently deducing based on available evidence? Apparently, the cockpit voice recorder was running the entire time (they have stated that the co-pilot or whomever was at the controls was silent the entire time). Had an attendant murdered the co-pilot in the cockpit, it seems likely there would be some evidence of that on the recording.

[TexasGator]

“Why would we not assume that the flight attendant called the pilot out, entered the cockpit and killed the other co-pilot and crashed the plane?”

We would have to assume the French authorities are lying about what is on the FVR.