They are both right IMO. I believe what Sixty Fiver means is that you should not attempt to set the forks on a carbon bike to stay at 130 mm like you can on a steel frame. What your friend probably means is that when you install your wheel, you can apply enough force to spread out the dropouts far enough to get a 130 mm hub in place. It will snap back to 126 when the wheel is removed, but it should be flexible enough to fit the larger wheel. If this takes a bit of effort, it may make wheel changing on the road (in case you have to fix a flat) a bit more effort. I suggest you borrow a 130 mm wheel and see how hard it is to do. Then you can make the evaluation. IMO, doing this should not be considered dangerous or harmful to the frame.