The Once-ler is talking to his conscience and he seems to feel really bad about his
actions. But then he reasons "Well if I didn't
do it then someone else would". This
reassures him and he decides to not change
his ways. Is this a good excuse for poor
behavior? Do you think humans think or say
this when doing questionable things?
in the first 13 minutes of the lorax

No

Explanation:

If someone says, "Well if I didn't do it then someone else would" that would mean they are trying to pretend that they shouldn’t be held responsible for their entirely voluntary actions. This doesn't affect others. This excuse is only truthful if everyone uses that excuse. This means your procrastinating. I think everyone thinks this. There are just so much people in this world, you think someone will do it for me. In the process, your behaviour changes. Stop waiting for the right time because the time will never be right, you just have to go with your gut and just start. The Onceler is thinking, I shouldn't change because someone else will fix everything for me. He is being lazy and has given up hope.