1. Nobody can prove the existence of a higher being. On the other hand, hard scientific evidence supports evolutionary claims and the big bang theory.
Hard scientific evidence supports the Big Bang theory. Who's to say a god didn't create the Big Bang or evolution? Atheism is as invalid as Theism, so I believe schools should teach neither. Evolution and the Big Bang are independent from anything religious, so it can't be used as an argument to support Atheism.
2. Intelligent design advocates claim that they're not promoting Christianity, but they would be. I don't think we'd hear any Hindu ideas in an American intelligent design class, do you?
3. I know this is going beyond the "official" intelligent design stance, but if they claim that god exists outside of science, why would they want to teach their theory of god in a science oriented classroom as opposed to a theology classroom?
Those are personal opinion, because creationism doesn't always mean Christianity.
4. The separation of church and state protects both America and the religions that have taken root here. Just because you believe in something neither makes you correct in your assumptions nor someone else's beliefs incorrect, and nobody should be allowed to dictate what everyone has to believe in. I think that it's a big enough sin that parents are allowed to instill in their children concrete ideas about religions, regardless of whether they believe in athiesm, Christianity, or the flying spaghetti monster. A spiritual journey is very personal, but I've no problem with parents bestowing upon their children a solid set of morals.
You are proposing that we dictate the classroom to teach Atheism. Also, morals are just opinions, everyone has different morals. It's the same as religion, so you are just proposing that we teach what
you think is best for everyone, which contradicts what you said a few sentences ago.
Take a look at D.A.R.E. (Drug Abuse Resistance Education). We've been taught at a very young age that taking drugs and drinking alcohol is bad for you. We've also been taught how to face peer pressure and how to avoid such situations. But look at society today. How many people are going against the teachings of D.A.R.E.? Cigarettes today kill more people than do alcohol, other drugs, heart attacks, car accidents, etc (I remember seeing this somewhere; I just can't remember where). Everywhere on campus, there's ALWAYS someone walking around with a cigarette in his mouth, and while I was a cashier at a grocery store, 1 out of every 4 customers bought either beer, wine, or pure liquor. If teaching things at school supposedly "convert" you, then nobody would be doing drugs today.
Also, take a look at Health/Sex Education. We've been taught almost everything (and perhaps even a little too much) about STDs, how to prevent STDs, and how to have safe sex. Like with Drugs, we've been told that the safest way to prevent STDs is abstinence. We've also been taught that condoms are also a method of preventing them too. But look at society today. How many people, especially teenagers, are resorting to abstinence? How many teenage girls get pregnant every year? And look at how many people today have herpies, AIDs, and all these STDs? Again, if things taught at school are suppose to "convert" you and prevent you from going against their teachings, then there would be no sex today or no STDs going around.
Another possibility is that these have always been around, but now that they have such a negative connotation, we are much more aware of their occurrences, which would actually mean that the education is working.
I don't think that the problem is that it converts you, I think the problem is that it's being presented as a valid scientific theory. To use your religion example, there's a difference between learning that some cultures believe in a certain god and learning that a higher power created the universe.
Atheism is not a valid scientific theory either, and they certainly don't teach agnosticism at school.
None.