We should be pro-life for the same reason we should be environmentalists:
“‘Image of God’ also elevates humans above all other created things, indicating their responsibility to provide a benevolent and ethical stewardship over the rest of creation.” (Faith Study Bible)
The kind of environmentalism that values humans over fish and dogs. But still, an unabashed environmentalism and stewardship and care for the massive garden God has given us dominion over.
The same reason we have to keep the air and streams clean is the same reason we have not to unnecessarily and electively and singularly murder unborn human beings: we are in the image of God.