"If we were explorers, we wouldn't need to be taxed to explore."
oh for Petes sake,
Building a machines like a Saturn V moon rocket or the shuttle is not something that gets done without taxes nor by a single individual.
Just as building a nuclear aircraft carrier or B2 Bomber.
And the many European explorers that came to America hundreds of years ago were funded by their leaders/kings/queens.
I think you are making assumptions. You don't give the private sector enough credit.
The reason that this sort of thing is not financed by private industry, (even though private industry actually does the work), is that most companies big enough to afford this sort of thing are not allowed to exist.
If a corporation gets that big it is very quickly suffocated and subjugated by our paranoid and overweening federal government. Bill Gates learned that a few years ago. He is however allowed to invest his money in non-threatening pursuits. For example, the Gates foundation donated about 5 billion on malaria vaccine research. Kind of a waste really, since DDT is the best malaria vaccine.
But if he had that money on space exploration...