I think there are plenty of people with less than zero ability to execute, i.e. a net negative contribution.
Would people who are passionate enough to really think things through with their idea contribute less than zero? I'm not talking about the fictional coked-out, fast talking movie exec with logline "business plans" that want 60% + a seat on the board. If you're talking with that kind of person, then of course you don't take it on.
The vast majority of people who are aware of a single great idea probably either heard it from some other party or just got incredibly lucky. People who can consistently come up with good ideas are a tiny minority compared to the amount of people who are aware of a good idea.
On the technical side, have you never worked with a programmer that insisted on introducing his favorite framework/language, or declared that the "current code sucks, it needs to be re-written"? That's potentially a negative contribution. Hell I've even been that guy. It's not only possible, it's common.
I think the negative influence is usually more in line of those who resist change such that so much cruft accumulates, that it truly becomes too dangerous to change anything.