Is there a word or phrase for something that one might wish exists, but most certainly doesn't?
Solution 1:
It's just a...
pipe dream - an unattainable or fanciful hope or scheme
Example usage from oxforddictionaries:
free trade in international aviation will remain a pipe dream
Origin: Late 19th century: referring to a dream experienced when smoking an opium pipe.
Solution 2:
You may say it is just wishful thinking:
- Thinking in which what one wishes were the case is believed to be real or likely to become real.
(American Heritage® Dictionary of the English Language)