Aikido comes from a long history of many different styles of jujutsu. Although not always in line with the accepted underlying philosophies of aikido, it is important to understand where aikido comes from. As such, every now and then my own exposure to traditional jujutsu does get mixed in with my aikido classes.
This is some tanto waza, or knife technique. Not defending against a knife, but defending against a potentially life ending kick from the attacker.
Here we are not concerned with justifying the use of deadly force or how much force is acceptable under current law. In this case, these techniques were designed to dispose of an enemy on the battlefield as quickly as possible, and we practice them through completion of the kata.