Answer: ideas aren't worthless.

An idea has no value to you if you can't execute, but it has long-term value if you might be able to do so in the future, and it definitely has value to competitors who may wish to execute it now.

[Edit: Also, "ideas are worthless" sounds like the speak of arrogant VCs who want to downplay the importance of entrepreneurs... I've never heard an entrepreneur make such a statement.]