One of the big reasons for a manned space program has been so-called technology "spin-offs" resulting from the program, but I think that they pale in comparison to the list of spin-offs that we receive from military technology. Here's a short list off the top of my head:
The Internet (Eisenhower created DARPA, and packet-switching was created as a way to maintain communications during a nuclear attack)
Electronic Computers (Alan Turing's "Bomb", ENIAC for ballistics tables, etc)
Rocketry and Jet Propulsion (The V-2, which is weird because it's a spinoff from war that made it's way to space)
Chemotherapy (Mustard Gas was the basis for the first chemotherapy drug)
RADAR/SONAR (a modern airport would be near-impossible without RADAR)
Nuclear Fission (energy production)
Submarines (another "spin-off" that has moved over to undersea exploration)
Plastic Exposives (used for construction, better than blackpowder)
Encryption (has been around for centuries, probably invented for military purposes)
Synthetic Rubber (such as Ameripol)
GPS is pretty pervasive too
All of these things have had a significant impact on our civilization, and to be honest, we wouldn't have a space program without some of them....It's just horrible that so many millions of people had to die for these things to come about. If a manned space program could provide these sorts of technologies, most people would be on board.......but ask them what the International Space Station has provided, and they would be hard pressed to tell you.