Uke is giving his body to shi'te for shi'te's benefit - whether in training or performance. In many situations, uke willfully places himself in a situations where shi'te could easily and seriously injure uke if he was so inclined. Inherent in that is a sacred trust that shi'te will safeguard his partner.
To place the ultimate responsibility for safety on uke within this paradigm is completely illogical.
But shi'te can make a mistake. Uke has to be always ready to avoid the damage, even if is unintentional.