In your example, you are presenting "I think you should spend $10 for an empty envelope" as a separate activity, and you are being misleading because you are not putting it into context and saying "I think you should spend $10 for an empty envelope, if this means you can get a full one".

With the justice system example, I am presenting the example in context--that is, I am not just saying "I think you should harm innocent people", I am saying "I think you should harm innocent people, if other people are helped more". It's the in-context version of the statement that I am presenting, not the out-of-context version.