The choice got harsher as time passed. When the Amish were founded, the outside society was very similar. People were very pious, most were farmers etc. But since the Amish form a time capsule of the 17th century, Rumspringa became more and more of a culture shock.
The Amish are definitely not a time-capsule of the 17th century.
They use technology but are quite selective about what will benefit them and what will interfere with their way of life too much to become a part of it.
It's true that the gap between the Amish and the communities surrounding them is ever expanding but they're definitely not standing still in time, just moving at a much slower pace.
The Amish system seems rather vile, but unless you totally take away people's right to associate and indoctrinate children I don't see how we can ethically eliminate it. I suppose mandatory education that includes proper science and so on might be a good first start.