In this quote, Thoreau is suggesting that despite the fact that we, as a society, have overcome many of our primitive fears and superstitions (symbolized by the hanging of witches), we still harbor irrational fears, represented by the fear of the dark. The "dark" could be interpreted as the unknown or unfamiliar. Though we’ve advanced in so many ways, there’s still an inherent fear of the unknown that persists.

This idea can be seen in the way we approach change or unfamiliar situations. Often, even when we know that old ways of thinking or acting are not beneficial (the witches), we still fear stepping into new territory (the dark). This fear can hold us back from embracing change and pursuing growth.

In today’s world, this could be applied to a variety of situations. For instance, in the realm of technology, there are many who fear the rapid advancements and the unknown implications they may have on society, even though these advancements could potentially solve problems and improve lives. Similarly, in personal development, one might be afraid to step out of their comfort zone and try new things, fearing the unknown outcome.

The quote is a reminder of the importance of overcoming these fears and embracing the unknown in order to progress. It encourages us to challenge our fears, to face the ‘dark’ and to embrace change, even when it’s uncomfortable or scary. Thus, it’s a call for courage, adaptability, and the willingness to confront the unknown for the sake of growth and advancement.