[wvenable]

I think you hit on a much better question! Just ask "are you passionate about programming?" and then ask them to defend their answer. If they code arduino robots in their spare time or simply love solving people's problems at work they have to convince you either way. That's so much better than trying to gauge their passion with a presumptive question.

[napoleond]

The problem with phrasing the question that way is that it's way too open-ended (and likely to make the candidate regurgitate the same BS from their cover letter, which is not the point). An interviewer's job is to make it as easy as possible for the candidate to prove themselves. If they don't have side projects, that's fine--there are other questions that will hopefully provide similar information (ie. "What project have you worked on that was the most satisfying for you personally?"). But the side project question has a high signal/noise ratio.