[Reiver]

Sporty machines tend to seduce their owners into fits of speed....I have to exert some self control on occasion when on a nice twisty public road.
I know a Porsche informal group that hits the back roads locally at felony speeds that have public traffic, blind corners, no escape areas (mtns)...basically street racing. They call it 'spirited driving'.
It's not just bikers or any subset....just folks a bit too secure in their own abilities and accepting a great deal of risk for unsuspecting others.