We already have a purpose, and its not flying a few people to Mars
It's like I noted some 10 years ago:
http://www.geocities.com/epgrondine
Recognize that manned spaceflight is tied to dealing with the NEO hazard, and then...
The only way back to the Moon is through ISS, and then only way to Mars is through the Moon.
The physics of the costs of launch limit the problem.
