What is the difference between sending humans, with all their implications, vs. instruments and engines to get them there? Why is the human part so important to science?
Because the desire to explore is an instinct most of us possess. It's not necessarily about science, although it's certainly something we will do. Exploration is in our genes. So why not send robots instead of humans? It does not satisfy. For the same reason we don't live in purely utilitarian houses, or have purely utilitarian cars, or eat tasteless nutritional gruel. That kind of thing is for oppressive socialist governments who try to fit square pegs into round holes. Forcing us all to exist in the same dull repetitive manner is contrary to human nature.
And at what cost, to everyone who must pay real money for the expedition, (...never minding the folks who volunteered their 'free time'/lives to go up first)?
No. I don't expect governments to do it. They're far more interested in maintaining their own strategic interests in orbit. But it would be nice if they got out of the way to let the rest of us do it instead of trying to get their pound of flesh out of the investors. They can impose their crippling bureaucracy on their own go nowhere space program.
Because space is mostly empty, and extremely hostile. There's no rational reason for anybody to go there.
So is the ocean. But hey, we got over it and now we have a global society. Every new area we haven't established ourselves yet is empty and extremely hostile. And I already gave you a very rational reason for going there.
Combating the Global Food Crisis
So we enable everyone to have more offspring...and then they need an even greater amount of food. Then we just end up back where we were. How long can we keep ignoring the fact that population is the problem. Global warming, peak oil, antibiotic resistant diseases, ozone hole, etc. All of it will just keep getting worse if we don't do something about our population.