Bible says thou shalt not kill.
No, it says 'thou shalt do no murder. That is nearly the same but not quite. After all, if Christians actually obeyed 'thou shalt not kill' there would be no death penalties, and no fighting in wars which have a tendency to kill people.
Life begins at conception because without conception we would not be here.
Life does, but 'not as we know it, Jim'. Sure the zygote is alive but think of the dangers it faces. It has to manage to follow the fallopian tube to the uterus and then manage to implant into the wall of the uterus - steps that many zygotes fail. Of course no one knows there is a zygote - its only some weeks after its formation and successful implantation that anyone knows its there.
The next danger for the poor zygote is remaining implanted. No all implanted zygotes make it - quite a lot disappear before anyone really knows about them. Then, throughout the pregnancy, the foetus might spontaneously abort. Even if it makes it through to 16 weeks it is a great deal different from a baby - it can't survive on its own, its brain isn't very developed etc. Really, a foetus up to that stage is better thought of a potential human.
Now, we need to remember, too, that no aborting a foetus might end up a lot worse. There is no right and wrong in this. If a baby is born to a teenage girl who hasn't the capacity or income to support it what then for the child? Or if the child is severely disabled from birth or has a disease that ends in a painful death in childhood? What about a person who is raped - should she have to carry the child of a rapist and be constantly reminded of that most dreadful crime?
This is no easy moral matter and one that needs to be considered carefully ofr each case. Blanket decisions are likely to be flawed.
Your assumption is that "God" has control over when people die. You don't think it is possible we were created but he has no control over what happens in our lives, like Honda isn't at fault if somebody driving one of their cars is in a car wreck.
Have you read Psalm 39 recently. I do recommend it. Verse 13 is a good place to start. Then say god has no control over what happens. The fact is the astonishing fail rate of zygotes does say something for the design of the whole system and suggests that either there is no designer or, if there is and it is god, he is not up to being worshipped.
The case against abortion isn't religious in nature, you want it to be so you can say that you aren't religious and thus it is ok.
Well, true, people make a case out against abortion who are not religious but mostly it is religious based decision. I have made the case for it above without reference to religion so I am quite happy to debate it with you on that basis but certainly, in most countries, the vast majority of people campaign against abortion are religious. (Apparently shooting to death doctors who do abortions is also religious.)