Look at it like this. A fetus is a seed, and an infant is a tree. All in a forest. But the forest grows too large. There are too many trees, and not enough people to care for them. But it’s wrong to cut down a tree because trees are precious. So, what do we do? We stop planting the seeds, and if we plant a seed by accident, or forcibly, we take the seed out. That is the choice of abortion in an overpopulated world. Adoption is not an end-all-be-all. A seed can grow into a tree, but it is not one.
First, the world is not overpopulated. Just because it seems that way in cities does not mean that the entire surface of the Earth is covered in a living mass of human beings. In fact, it is mostly empty space. A 2003 assessment by the United Nations agrees. The UN projects, under its medium-growth scenario, that the human population will remain relatively stable at 9 billion until the year 2300 and then begin to decline.
But the real issue I take with your argument is that, once again, it relies on the dehumanization of prenatal children. You have now added ‘seed’ to the many dehumanizing terms used to describe these children. They are also routinely called parasites, unwanted invaders, tumors, and clumps of cells.
The pro-life position is that prenatal children, including you and I when we lived in the womb, deserve the exact same human rights protections granted by the 14th Amendment to the Constitution of the United States that the post-born receive. From our perspective, ‘taking the seed out’ is no different than killing an infant, or as you put it ‘cutting down a tree’. We consider both precious.
Also, there can never be a tree without a seed. A seed is simply an early stage of life for a tree, just like a sapling is. It is not a different organism. Just like an embryo and an adolescent are both still human. Killing at any stage of life ends the same exact life consisting of the same exact DNA.