There is a difference between thinking something is a bad idea because it's hard and thinking something is a bad idea because it's dangerous. Your Stripe example is an example of something that was hard. Mighty is an example of something that is may not actually be hard but is most likely dangerous.
The problem is that early on dangerous and hard are sometimes synonymous; people argued Uber was dangerous, and in some cases, it was - relatively unvetted drivers driving people around the city without a taxi license. But now it's changed how we move about the world.
It's hard to predict how the end of a startup will look from the beginning, but ambitious ideas often look dangerous, scary, hard, or impossible at the beginning.
