Space Exploration vs. Disease Eradication

I always had this at the back of my mind but never thought about it really seriously. The recent launch of a NASA spacecraft to a distant celestial body.....yeah that was the crashing with a comet, 'to study the constituents of a comet' is what re-ignited the question in me.

I dont remember the figure but it sure was huge. The cost the Americans are willing to pay for space exploration is more than enough to eradicate many prevalent diseases and accelerate the research for AIDS and Cancer.
I wonder how do grown up people in general and the congress in particular, is willing to spend this much to 'study what the comets are made up of and further our knowledge of the universe'. What the heck do you do AFTER you have known all there is to know about the universe. Can you change it, can you alter it. Of what use is it to spend precious resources to go out of this planet when we havent done enough to make it the best place to survive in.

Go out into the space, explore the frontiers of the universe.....but do so only after you've made the earth a paradise and there isnt much left to do, down here.