But it could not have been avoided. It was part of the plan. It was needed to convince some that his love will conquer everything, even the power(terror) of death.
You also forget that these people were waved off by their teacher, warned repeatedly of what was in store for them. But what they experienced first hand was so compelling they could not be swayed from their appointment.
Also, of personal concern to the people that went to their deaths singing Psalms of Praise, was the clear warning that if they denied what they saw, it would really offend the guy putting on the "banquet", offense to they point of where they might be asked to vacate the premises...