Responsa sur La Genèse 9:7

On the other hand, however, there is room to forbid aborting a fetus or killing it based on that which is written in the Gemara: Any [Jew] who does not engage in being fruitful and multiplying is considered as though he sheds blood, as it is stated Whoever sheds the blood of man, etc. (Genesis 9:6) and it is stated [adjacent to it], And you, be fruitful and multiply (Genesis 9:7). […] Ben Azzai says, “It is as though he sheds blood and diminishes the Divine Image.” […] The Sages taught, “And when it rested, he would say, ‘Return, Lord, to the ten thousands of the thousands of Israel’ (Numbers 10:36). This teaches that the divine presence does not rest upon less than two thousands and two ten-thousands of the Jewish people. Consequently, if there were two thousands and two ten-thousands of the Jewish people, less one, and this man did not engage in being fruitful and multiplying, is he not found to have caused the divine presence to depart from the Jewish people?” (Yevamot 63b-64a) And if these words are said about someone who is not engaging in being fruitful and multiplying, who is not doing any actual action, all the more so [is it true] about someone who does an action that reduces the possibility of the existence and growth of a Jewish life! And there is no doubt that this was the intention of Tosafot, which we cited earlier, when they said that it is forbidden for a Jew to kill a fetus.