What is ironic about Boxer’s response to the executions?

It is ironic that Boxer believes himself and the other animals responsible for the executions...... that Napoleon is blameless. Boxer's response to the executions is to remove the evil among them by vowing to work harder.

Only Boxer remained on his feet. He fidgeted to and fro, swishing his long black tail against his sides and occasionally uttering a little whinny of surprise. Finally he said: "I do not understand it. I would not have believed that such things could happen on our farm. It must be due to some fault in ourselves. The solution, as I see it, is to work harder. From now onwards I shall get up a full hour earlier in the mornings."