insistence that an object in motion... ;-) Any obstacle that the
front wheel hits taller than halfway up or more to the axle is likely
to cause "bad things to happen"
Which could really only happen if you weren't paying attention. Fortunately
they're somewhat self limiting on speed on rough surfaces - as in grinding
to a halt.
Then again, "I ain't skerd" to ride anything. My favorite bike is
the penny farthing with a 4' front wheel. Now THAT thing will endo!

And those things produce the mother of all endos (starting with your
head about 10 feet above mother earth). Never rode one, but would
love to some day.
One has to be especially careful descending hills; sufficient grade will
quickly put you ahead of CG and over you go - and as you say, it's a long
fall. It's no wonder the newer bicycle designs are called "safety bikes"!
But it's the most fun inanimate thing I ride.
http://www.johnnyhouse.com/images/sayhi.jpg