Is it wrong that I want to tell my brother he's wasting his money?
I don't think so, do you think that it will help if you tell him that?
It means I can keep his money that he supposedly is "throwing away".
It's good to tell your family members the hard truth, if you think that it will help them in the long run. However, it sounds like you are planning on convincing your brother to give you money instead of spending it, which is deceptive, and unfair to your brother.
I have no plan to give him back the money. He's a pushover.
Stealing from family is one of the worst things you can do, and if he catches you he will be very disappointed and will probably resent you for a long time. It's not worth it so don't do it.