The only thing distinguishing a fetus from a human these days is a fancy, made-up definition.

Actually, it is a physiological difference from other stages of development of the human organism: a fetus doesn't breath. It's also not a physically-independent organism, it's attached to another (adult, female) human. Those two characteristics alone are enough to distinguish a fetus from every other category of human (newborn to adult). Fetuses are also a specific age, specifically, the 9th week after fertilization extending until the time the fetus is born—whenever that is.

As I said, there's nothing wrong with placing a fetus into it's own category of what constitutes a human, just like we do already with newborns, infants, toddlers, children, pre-teens, teens, young adults, adults, middle-aged, and the elderly.

We also have different sets of laws for all of these categories. (For example, the elderly get free health care, teens can't have sex with young adults, adults, and older, and people under 21 can't drink alcohol outside the home, etc.)

There's no contradiction with deciding that a fetus is its own category, and still saying "you can't kill a fetus". But trying to win the argument by saying a fetus is a "full human being in the womb", and that's why you can't kill it, as you suggest, isn't going to fly: you can't win an argument simply by redefining the words that you use, by eliminating distinctions that do, in reality, exist, so that your own preferred morality becomes the only choice.

Actually, you seem to be endorsing "word play" by trying to deny that such a thing as a "fetus" even exists, even though literally every single person reading this comment knows what a fetus is, and knows that it's not a newborn, adult, elderly, or any other category of human you seem to want to combine it with.

That fact that everyone can distinguish a fetus from every other form of human is prima facie proof that "fetus" as a category of humanity is valid. What laws should apply to a fetus are secondary, and must be established independently, not by trying to merge it with some other category so that your preferred set of pre-existing laws apply.

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As an aside, efforts on the pro-life side to make human-ness the defining, end-all be-all attribute that gives an organism a "right to life" are misguided as well. We recognize numerous situations where humans do not have a "right to life". Here's a few:

- The human has committed first degree murder, and been sentenced to death in a jurisdiction that does capital punishment. That human no longer has a "right to life".

- A human is attacking another human, and is killed in self-defense. That human also does not have a "right to life".

- You're at war. Any human acting in a military fashion on the other side, who has not already surrendered, does not have a "right to life". You can (and are supposed to) kill them on sight.

(And there are more.)

So, merely being "human" does not grant an organism a right to life. It's always a contingent right, and obviously "up to the humans who create and enforce the laws", not on some universal law or morality or whatever. We take away the "right to life" of other humans whenever it seems right or necessary to do so.

Given all that, a fetus is clearly a human organism in a bit of a pickle: it can't breath, it's physically attached to the mother, for much of it's time as a fetus it's not even viable outside the womb, etc. There are clearly two humans involved whenever we are talking about a fetus, which if you'll notice in the examples earlier where a right to life does not exist, is a feature of all of them.

IMO, pro-lifers would get farther if they treated human fetuses as the separate category they actually are, and built up a case why we should curb some or all of the rights of the other human involved, in favor of the fetus. I believe such an argument can be made from first principles, not by appeal to a non-existent "right to life" that supposedly all human organisms have (even though they don't, as show above).