A) Because every dollar invested in the US space program since inception has created about $7 of economic benefit to the consumer economy.
B) (Related to A but worth mentioning separately:) Because the space program has led to major advances in medicine that have improved length and quality of life on Earth. [1]
C) To gain access to essentially limitless energy resources via space-based solar.
D) To gain access to material resources (e.g. minerals) that are scare or absent on Earth. [2]
E) To create an off-Earth breeding population of humans so that one asteroid / plague / nuclear war / whatever cannot wipe out the entire species.
[1] Here's a simple example: When the Hubble telescope was initially launched, it had a small lens defect that blurred the pictures slightly (the pictures were still better than any Earth-based 'scope, though). Image processing software was developed to clean up the pictures until a replacement lens could be deployed. That software then migrated over to MRI machines where it is now used to detect tumors much earlier than used to be possible.
[2] These resources are better accessed from the asteroids than Mars, but going to the latter gives you access to the former.
There were myriad new materials and other technologies developed to defeat the challenges of getting into and surviving in space, many of which launched companies and industries.
Some commonly cited examples: memory foam (TempurPedic Mattresses), better water filters, freeze-dried food, cordless power tools, various plastics, useful solar cells, carbon fiber epoxy.
On top of that, there are all of the benefits of having satellites (telecommunications, GPS, satellite TV, etc).
you raise a bunch of economic issues, but the poster to which i replied simply stated that there was "no where else to go", which is absurd
the rest of your points are dubious. your point B) has been proven false since the launch of the space station...this was one of its apparently initial goals, zero-g bioresearch...except that ended up being replaced with simulating everything in computers with bioinformatics on earth much more easily
C) also has no meaning as we could provide 100% of our solar needs by simply covering a part of any of our major deserts with solar thermal.
B) (Related to A but worth mentioning separately:) Because the space program has led to major advances in medicine that have improved length and quality of life on Earth. [1]
C) To gain access to essentially limitless energy resources via space-based solar.
D) To gain access to material resources (e.g. minerals) that are scare or absent on Earth. [2]
E) To create an off-Earth breeding population of humans so that one asteroid / plague / nuclear war / whatever cannot wipe out the entire species.
[1] Here's a simple example: When the Hubble telescope was initially launched, it had a small lens defect that blurred the pictures slightly (the pictures were still better than any Earth-based 'scope, though). Image processing software was developed to clean up the pictures until a replacement lens could be deployed. That software then migrated over to MRI machines where it is now used to detect tumors much earlier than used to be possible.
[2] These resources are better accessed from the asteroids than Mars, but going to the latter gives you access to the former.