Even if you think Space travel is worth the money (which I personally do), adding humans to the mix makes projects incredibly more expensive. Even in the realm of space travel and research, sending humans is a questionable use of the money.
It's nice that we can send humans to space and it's good to keep that capability going so that the knowledge doesn't die. But the unmanned missions tend to pull the weight of actually accomplishing useful things. Humans just get in the way.