Why does the Catholic Church excommunicate those who it feels have gone astray? Aren't they putting themselves above God?

I've gone astray most of my life, yet I've never been excommunicated. I think referring to one who simply is astray as worthy of excommunication, is a bit simplistic. Most Christians are "astray" and NEED the Church to help guide them. So I think your definition of how one becomes excommunicated isn't necessarily accurate.
However there are those who are excommunicated from the Church and there is a misconception that this is done in a "vindictive" manner. That simply is not accurate. It's actually done in a medicinal manner, for those committing grave offenses, in order to correct them and bring them back into the path of righteousness.
God is our father, and any parent understands the importance of tough love, every once in a while. You hope it never comes to that point with your children, but there are those extenuating circumstances where you have to impose a punishment on your child out of pure love.
Excommunication is meant as a medicine to inspire people to repent and be reconciled to the Church.
I think a simplistic example would be....if I sat down with 2 children to play a game with rules. One child plays the game, making mistakes from time to time and I as their mother, corrects them along the way. The other child refuses to listen to me, cheating at every opportunity and refusing to obey the rules of the game. I love these children, but I cannot allow the defiant child to continue playing the game with us, for obvious reasons. So I exclude that child from playing, until that child understands and realizes that he doesn't need to be a perfect human being to play, but he must at least make some effort to play by the rules, as opposed to cheating and defying them.
That maybe a simplistic way of explaining excommunication, but I think you can at least get a basic understanding that it's not done in a sense of vindictiveness. It's actually done out of love and concern for those who are blatently defying the Church.

I’m sure I heard a grab from the Howard gov’t about giving school principals some freedom to dismiss poorly performing teachers . I suppose that could be of some concern to those who might be inclined to economize with lessons on core subjects to make room for teachings of the gospel according to Rodney C & his ilk .
When added to the above the prospect of catholic schools being able to exercise that pesky freedom of religion thing in an effort to better maintain certain core moral values , The road to the city of Sodom could become intolerably steep .
Gosh , Worrying times indeed for poor Rod .

"I would ask you, if you haven't already, to read the New Testament. I think there are far too many witnesses and too many miracles to reject" says CatholicMom03.

In recent times there have been many "witnesses" to alien landings and kidnappings of "earthlings". There have been numerous "sightings" of the Loch Ness monster and some people long after the events in the Bible apparently have been visited by the Virgin Mary. The phenomena these so-called witnesses see can be explained in more rational ways.

For a start, people are able to construct what they want to see and experience. This explains False Memory Syndrome where some people, apparently victims of sexual abuse, actually experienced no such abuse at all. Witnesses in criminal trials today can be unreliable. This is also the case with witnesses two thousand years ago.

Secondly, in the era of Jesus Christ, modern scientific explanations were unavailable to His contemporaries. So, for example, He appeared to raise Lazarus from the dead. They didn't understand that Lazarus was probably in a coma. Not to mention that fact that the life of Jesus Christ was written years after He died. Historians are always wary of totally believing accounts written long after the events in question.

Also, if the Catholic Church wishes to teach that miracles are real, how can they also teach science? For example, either the solar system is a miracle of God or it can be explained scientifically. If the Catholic Church opts for the former then they have no business in education and should concentrate on proselytising.

On a positive note, at least the Vatican now acknowledges the Earth goes around the Sun. But that took a while, didn't it?

David, there are those, whom when confronted with video surveilance of an event, will still deny the event took place. As one of the biggest skeptics, I understand how difficult it must be to accept Christianity. As we all know, there are those already denying the Holocaust ever happened. I cannot imagine my life without my faith. I understand the power of prayer, because I've seen it work in my own life. Sounds like we simply will have to agree to disagree, and I wish you well!! :-)

Dear CatholicMom03 (I feel like we're old friends), you are right in that we won't convince each other. But I will say that there are three basic ways of looking at events:

Firstly, they can be explained. The Holocaust is one of those events where a combination of countless documents, witnesses and perpetrators provide rational accounts of why such a terrible event took place.

Secondly, they can't be explained...yet. The Black Death in 14th Century Europe was originally thought to be punishment from God or the work of Jews or some other non-rational idea. Now we know it occurred due to bacteria carried by fleas which infested a species of rat and was highly contageous. And assisted by filthy living conditions in that era.

Thirdly, they can only be explained as the work of some supernatural force.

Any education system which wants to maintain its credibility opts for the first and second ways of interpreting events.