Imagine if all the world's resources currently used for defense and war were reallocated towards...?

research in Medicine and Science, would we find a cure for Cancer and AIDS sooner? Would we develop an alternative fuel and do away with oil for good? Would we start to colonize space and other planets? Would the world be much better off...?

Wow! Wouldn't that be wonderful. I would hope more money would go towards education, too.
It certainly would be better for humans, but would the plant and animal life still suffer because of human selfishness?

Maybe. But then we'd have nothing to defend ourselves with when the aliens attack us!

In the order you asked:

Probably.
Maybe, and maybe?
Probably?
Yes.

And to the question you didn't ask - is it going to happen?

Not bloody likely. Man is a quarrelsome, antagonistic animal. Fighting each other is what we do. And all the good wishes aren't going to change that. The most peaceful society I know of would probably be the Old Order Amish, and they have their own problems with this. They just tend to keep to themselves, and not show their troubles to the outside world, is all.

If you ever try to reform the human race to get rid of violence, don't do it by stopping man from fighting. Do it by channeling that energy and conflict into some other means, where they can still struggle and compete, but nobody gets seriously hurt - most of the time. Heck, we do that now. It's called Major League sports....

Except for space I think I'll take butter and give up the guns. We are water creatures living on the only free water in the system. There is no getting to the stars because time in space kills humans. Just get used to being here. The first thing they look for on other planets is water. If they would check out the rear view mirror they would see how foolish that is.

The only government that keep taking your money when they no longer have to are socialist. Taking the people's money to allocate toward any of those goals is much less effective, anyway, than letting the laissez faire market loose on a problem.

But it is that very same socialism that prevents letting loose the genie of the laissez faire market. Governments prefer to be controlling--and that goes for our own.