This is pretty much my assessment, when the child can survive outside the womb.  That is when you can without reservation say that the child is "alive." 

I mean by a very technical definition, every egg and every sperm is alive, so I really don't see why people draw the line at conception.  So technically you are killing future babies using condoms or taking birth control!  The logic kind of defeats itself eventually.

The other strong case is for when brainwave activity begins (somewhere around the end of the first trimester).

Development begins at conception, but "life" doesn't begin until much later.  Technically, the cells were always living, so just saying that they are alive doesn't do the trick.

I call bull on that. Most religions that actually make issues against abortion don't extend their beliefs to non humans. Heck, many of them don't extend those principals to humans outside of their religious affiliation. I haven't consulted my sperm, but I've never found a priest tiny enough to baptize them so I'm going to have to assume they have no religious affiliation of their own.

Besides, under that line of thought, not having rampant promiscuous sex would be the same thing, since sperm and egg cells are constantly being generated and dying off. I'm not sure if I recall this correctly, but I believe women actually have a finite number of egg cells that are cycled through, and menopause is the point at which egg cells are no longer being generated. Could be totally wrong or oversimplifying that point though.

To further that line of thought though for those that aren't religious, if you actually are attempting to defend egg and sperm cells on their own, you'd also need to not use soap, and die from starvation, since you can't eat animals, or plants which are also alive.

I don't disagree with your point personally, but I can understand where those who believe conception is the beginning do. Most people are attempting to protect a human life. No egg or sperm cell is going to spontaneously generate into a human on its own. Neither has the potential to become a human on their own, but once the connection is made and teh egg is fertilized, a human life can be made.

Are single celled creatures like Amoebas alive?
Do we consider parasites that can not survive without a host to be alive?

So, basically a sperm or unfertilized egg are (infact) Alive and so is a fertilized egg ...

When does it become unethical to kill a living creature, and when a living creature becomes a human being are two seperate questions; I think most people would agree that it is fairly unethical to kill a living creature that is not causing you any harm, and the killing of it does not produce any personal benefit, long before it becomes a human being though ...

 If sperm were identical to single celled amoebas you would have an amazing point. However they are not, so your definition has a hole right there. The bigger hole is that we do not consider all parasitic creatures to be alive by default. Viruses are not considered alive for example. Taking the requirements for what is considered alive or not on the special level and applying it to an embryo simple does not work.

What you are saying is my point, that simply saying life begins at conception is kind of an arbitrary decision because both the egg and sperm were alive before then.  The logic doesn't follow through and should be based on a different set of criteria.

Development begins at conception, but "life" as we define it does not begin there.

I think perhaps the question could be better answered if we defined what exactly we meant by "life", so we could better answer when it begins.  Someone up above said that perhaps it is when self-awareness arises.  However, one is not self-aware if one is, for example, asleep (sure, you could be when your dreaming, but not otherwise).  So we'd be forced to conclude that it wouldn't really be killing to cut off a sleeping man's head.  Now, since we won't agree to that consequence, we'll have to use some other definition.  If an entity can support itself, for instance, outside the womb, and thus has life, then any instance of of the body being unable to support itself would be disqualified as living, such as simply being on dialysis.  Again, we won't agree to that definition because of that.

Now, one might argue that a person could wake up from his sleep, or be granted a kidney transplant, and thus has the potential to be self-aware and self-sustaining, and define life that way, so we could conclude that the two above cases are indeed living beings.  That would grant to the moment of conception such potential too, and thus one would have to conclude it too is living.  However,

Unfortunately, the definition I have for human life is going to be whenever the "spirit" enters (er, sorry for the religous answer); when exactly that is I would have to conclude it would be before the moment of conciousness, per the above reasons, and since it would seem somewhat arbitrary (if nothing else) for it to enter just any time before that, I will have to conclude at conception.  Also, I want to be on the cautious side.

What is this "spirit" thing you talk about, which apparently magically exists before consciousness?

If we're going to throw science out the window, we might as well ignore everything we know about conception, which would render the anti-abortion argument useless anyway. No point in forbidding something we don't know is happening.