Family planning by using contraception disturbs the natural process of reproduction. The natural consequence of having sexual intercourse is conceiving a child, it is therefore wrong to interfere with this, and so contraception is intrinsically wrong.
If somebody wants to plan accordingly when they choose to have children, they must not engage in sexual intercourse as the reproduction of children is the natural purpose of engaging in sexual activity. The influential Christian theologian Thomas Aquinas preached that because sex was a natural act prescribed by God, any use of contraception was unnatural.
Human beings are designed to multiply naturally, without birth control to hinder their natural population expansion. We should respect the body’s natural reproductive purpose and stop fighting attempts to get pregnant by using contraception for family planning.