We will be going to space for scientific purposes, manufacturing purposes, and probably to collect resources. I don't see us building O' Neil Cylinders because living space on earth becomes scarce. I am actually concerned that humanity will "family plan" itself into extinction. Some people take the view that natural selection will kick in and eventually the earth will be mostly populated by humans who instinctively want to have big families. This will cause fertility rates to turn around and start rising again creating a need for off-world habitats. This view assumes that within our genes is code or at least the potential for code that creates within us a desire to have many offspring. However such code wasn't necessary to get us to ~7.5 billion humans today. Existing, tried and true code creating a desire to engage in the procreative act worked well enough until technological highly effective birth control came along. Modern birth control is a recent development which hasn't been around long enough to know the full ramifications its existence will have on humanity.