It's the sidecar racers that give me the willies. And the sheer unevenness of the TT course at 210MPH. In close proximity to dry stone walls.
Motorbike racers are, generally speaking, a sandwich short. My B-I-L, who races speedway, has broken his back three times- he's 4 inches shorter than he was when he was 19- and various other legs/arms/wrists/collarbones at various points in his career. Will he give up?
No.
Another friend still razzes around on a 25-odd year old RD350LC (the renault 5GT turbo of the motorbike world) with scars that make me feel queazy.