It depends on how narrow and how stretched you want to go. If you're trying to fit a stiff sidewall 35x12.5X17 on a 7" inch wide rim that bead is not going to be seating well on that wheel. I doubt it will break the wheel as they are built fairly well, but airing down or just normal driving will cause issues. Some of those issues are abnormal tire wear, lateral stability, excessive tire wear, ect. Possibly bead blow out if you're airing low enough in some terrain. Now .5" difference in "recommended" wheel width is not something I'd be overly concerned about; it could fit well if it's say a 285, but then again the manufacturer has a reason for recommending you don't go much lower than that. I probably wouldn't run it, but others have with no significant issues.
I wouldn't say I'm "afraid" of it, but there's a reason why the manufacturers are saying to use that particular width range and it's not just so they can sell you more tires. As for those Stretched tires, I've seen plenty of them blow out from worn sidewalls, damaged rims, ect. But then again, that's what happens when you stretch a narrow tire on a wide wheel.