It's not made up. Most modern radial motorcycle tyres use one continuous steel band, it starts on one side of the tyre and is wound through the tyres profile until it ends on the other side.. When you ream the puncture site you cut this band, therefore it no longer has that continuous single band and the tyres integrity is compromised..
Michelins are not made in this way, therefore tyre integrity remains when a 6mm hole is reamed..
I've done a trackday on a repaired tyre, and toured Scotland, twice, in winter on a repaired puncture, not a Michelin either..
Does anyone actually know anyone whos tyre has ripped apart under them and launched them into tree because of a puncture repair? Who benefits from all the scaremongering? The very folk who are telling you that you sleep with the devil if you roll on a repaired tyre, the tyre manufacturers.