Outer Space Settlement Killer Apps

The most obvious reasons for space colonization (to deal with resource shortages and to take care of satellites) are technically obsolete.

Another possible use is regulatory arbitrage, i.e., escaping obnoxious laws. This comes in two varieties:

1. Escaping laws against activities that people do not want nearby. Problem: competition from places on Earth (Las Vegas, Switzerland, or even seasteading or Antarctica)
2. Escaping laws against activities that people do not want anywhere. Problem 1: Colonies in deep space are sitting ducks and planetary surfaces are almost as easy to bomb as Earth's surface. Problem 2: Do you really want to help Roko's basilisk?

The best guess for a killer app is zero-gravity tourism. (We might even have zero-gravity residence as in “Abercrombie Station” by Jack Vance.) It's something unavailable on the Earth. Once we have a demand for large amounts of mass in orbit, it will make sense to have asteroid colonies as well to supply them. The asteroid colonies in turn might also be used to regulatory arbitrage since they are more defendable than either deep-space colonies or planetary surfaces.