I'd call it an interpretation, not a theory. But clearly the conflicting inputs was a UI problem, and while there may be tradeoffs, a better UI could have prevented the AF 447 crash.
This really won't die. It's clear if you read the accident report (linked in another comment) that the plane was already doomed by the time that conflicting inputs were potentially a factor.
You normally can't stall an Airbus aircraft, except in cases where the flight mode changes as it did in this situation. This was a huge part of the problem, an emergency occurred and the pilots were effectively flying an aircraft they hadn't flown before.
Fully pulling back the stick is what you'd normally do in an Airbus to gain altitude. It's guaranteed not to stall the plane.
UI issues contribute to situational complexity, stress, ambiguity, and failures to respond appropriately to circumstances.
And whilst the BEA report ... rather inexplicably, frankly ... fails to mention the inputs issues, it does address all the other factors I've described here.