I'm going to call someones wish stupid and say they shouldn't wish for it.
Why don't you like their wish?
It's stupid because it's not going to come true. For instance, nobody can wish for a 500-inch TV set.
Even if you think someone's wish is unrealistic, telling them that it's stupid doesn't do anything helpful. People don't necessarily expect their wish to be realistic, it's just something fun to think about. Raining on someone's parade like that will just make them annoyed with you and think you're a mean person.
Maybe I should rethink my strategy.
I think you definitely should rethink things. It's not very nice to call someone's wish stupid.