Just expanding the fear of the unknown point slightly, I've known more than one microlight pilot worried about landing on tarmac.
Come to think of it, given my Raven has no ground brakes, I'm one of them on occasion. Landing (or taxiing) downhill on tarmac can be thoroughly exciting in a way that grass isn't.
At the end of the day, we're all comfortable with what we're used to.
Incidentally I once did a precautionary landing into a long, slightly uphill, whitish field next to a chalk quarry. From the air I thought the white colouring would be chalk through very thin grass. I now know that landing on semi-refined sewage is very slippery, and it takes a very long time to clean the aircraft afterwards.
G