Reading about Air France Flight 447, to quote Wikipedia (emphasis added):
... A second consequence of the reconfiguration into alternate law was that stall protection no longer operated. Whereas in normal law, the aircraft's flight management computers would have acted to prevent such a high angle of attack, in alternate law this did not happen. (Indeed, the switch into alternate law occurred precisely because the computers, denied reliable speed data, were no longer able to provide such protection – nor many of the other functions expected of normal law). The wings lost lift and the aircraft stalled.
But whether an aircraft stalls or not has nothing to do with its airspeed - the only things that matter are the wing's angle of attack and configuration (e.g., are the slats extended? is the leading edge damaged? have we got ice on the wings?). The aircraft's configuration was completely normal, and the AoA vanes were unaffected by the blocked pitot tubes (as evidenced by the fact that the aircraft's stall warning correctly sounded due to its excessive AoA during the period of time that the pitot tubes were blocked and valid airspeed data was unavailable). Why does the A330/A340 disable high-AoA protection in alternate law if airspeed data is lost - even if AoA data remains perfectly valid?