Indeed accountability is the mainstay of discipline.
One should always remember that Aikido is also designed a vehicle for personal
transformation, striving to better one's understanding of self and actions. Creating
value in your life means taking responsibility for your actions. A Sensei should not
judge the student for mistakes, but offer correction and keep the student
accountable for his actions and the standards of the dojo. If that means that
habitual tardiness means being sent home, then so be it. That is accountability.
Being habitually late or having a casual thinking about such issues is as
disrespectful to yourself and others, as it is incredibly selfish.
Respect runs both ways. I'm an adult, and I expect to be treated as one without having to defend my actions under the threat of being "sent home" like an 8 year old.