And if two pitot tubes read 0 kts and one reads 350 kts what is the speed?
If you have WOW probably 0 and one binnable pitot, at FL 300+, 2 are probably frozen and the other is probably nearer the truth but possibly also a bit iced and therefore not 99.95% reliably accurate.
So what to do. 9 times out of 10 the AP could probably safely fly pitch and thrust and descend to below FL350 based on more relaxed numbers, machine experience and probabilities. Maybe 99 times out of 100. Could even broadcast a Pan Pan for you and check for collisions.
But!