Cause and effect.
For example. There are materials to build a fire. If you take away the critical components to build it, there will be no fire.
If you clip a bird's wings, it will die in the wild.
If you have all the components for conception (sperm, egg, etc.), and you sterilize the egg, there will be no life; if you sterilize the sperm, there is no life. Destroying critical components for life is tantamount to taking life.
We have the technology to ensure that conception takes place correctly, so given that, destroying the critical components is tantamount to taking a life...