How these cars were "meant to be used" is actually a very interesting question.
You could say that since they were street-legal and came with bumpers and weather equipment, they were supposed to be street-driven, all-weather transportation that would be parked where bumpers would be needed.
Since they were marketed as "sports cars" (that were street-legal and had weather equipment and bumpers), they were meant for sports car club events such as road rallies, something that was very popular in the 1950s and 60s.
Since performance options were offered by the factory, you could say that they were, on a rare exception basis, also meant for racing. (And if they were meant primarily for racing, they would have come without bumpers or weather equipment, and probably a cut-down windscreen and an all-aluminum body ... they call that one the 100S.)
I'd say that they were meant primarily for street/road driving and mild competitive car club events on public roads. Anything else was an exception, and to say that thrashing them in "historic" rallies is all well and good if you really want to do that to a street car, but the factory entered them in grueling competitive events only for the publicity that resulted, not as a demonstration of how they were "meant to be used."
If Europeans want to laugh at the way we use ours, I'd counter that it's a pity they are thrashing and crashing and hyper-modifying these dear old street cars, using them up and losing their originality in exercises of willful self-indulgence. And how can we change that? We probably can't change that, but thankfully they can't stop us from enjoying and respecting our examples and preserving them for future owners to enjoy.