Re: abortion issues
Gammaknight, I think you're still making the same mistake that causes all the problems in this debate. You still believe something has to be 100% a human being, or 0% a human being, with nothing in between. You don't realize that something that can be close to being a human being, but not completely one.
What you're actually doing here is increasing the definition of "human being" to include embryos, with the intent of turning around and saying "Ah ha! you agree it's a human being, so now you have to agree it's not okay to kill it, because we all agree it's not okay to kill human beings!" You're trying to make use of the fact that we agree it's not okay to kill human beings, but what you need to keep in mind, is that some of the people who agree to that don't think embryos are human beings. If you change the definition of human beings to include embryos, then you no longer have the universal agreement that it's not okay to kill human beings. Similar to if you change the definition to include insects, then there'd be plenty of people who would think it's okay to kill human beings (of the insect variety).
As to environment, it's not just that the infant is inside the mother, but rather that it's still a part of her. It's not yet an independent creature. If you think being inside a car is the same as being physically and biologically attached to another creature, you drive a different sort of car than I've ever been in! ;)
At the end of the day, the things that make us think its wrong to kill people are the qualities people have. Things such as (but not necessarily limited to) sentience, desires, comprehension, etc. It's not the DNA. If a robot had all the qualities of a human being, but was made from metal, it'd be wrong to kill it too. Or if an animal had all these qualities, it'd be wrong to kill it (and I would say many animals do have some degree of them, but that's another topic). It's not really the fact that it's 'human' that matters, but rather the fact that it has these qualities that we value. An embryo does not have all of these qualities. They really are something different.
What you seem to be doing is trying to equate a single cell with a full grown adult. But they are very, very different qualitatively. They are very much not the same thing. They have very different properties.
Also, you seem to be ignoring the issue of degree. You're saying "this small difference isn't something we find important, so this huge difference of the same type shouldn't matter either." An anlogous argument would be something like "That building on the right is someone's home. The one on the left is just the same, except they haven't finished painting one room. We still consider them both homes even though there's a difference of completeness. So completeness clearly isn't important. These two nailed-together two-by-fours are just less complete than those buildings, but we've decided that completeness isn't important, so these two two-by-fours are a home too."
One more time: you're looking for a binary switch, when reality involves a continuous dial. All things don't fit perfectly into 100% and 0% boxes. Some things are somewhere in between.