Every human has the right to pursue a valuable future. This view is almost universally supported, with the exception of those that are deeply prejudiced and racist. Despite the scientifically proven fact that all humans are 99.9% genetically the same, white supremacists and nazis alike are unwilling to accept human equality rights because they feel that their genes are superior.
However, for the non-closed-minded and non-problematically-conceited, it is universally believed that every human has the right to pursue a valuable future.
This belief parallels the United States Declaration of Independence in that one has the right to "life, liberty and the pursuit of happiness." However, in violation of United States law, these rights are taken away when one is put in jail. A life in jail is still a life, though resources for pursuing a valuable future in that life are scarce.
By the successful use of any form of contraception, the combination of sperm and ovum is prevented. Therefore, the sperm and ovum have been deprived of a valuable future such as one that free people's experience.
Part of what makes one human is their potential to pursue a valuable future. Though monetary obstacles often come into play, truly free humans are otherwise able to pursue any action they deem as valuable.
I, for example, take great pleasure in consuming macaroni and cheese. For me, the ability to make my favorite food is part of building a valuable future, a future in which I am happy because I have done something (made and consumed macaroni and cheese) that I see value in.
When one is murdered, their loss of life can also be described as a loss off a valuable future. One who is no longer alive certainly cannot pursue a valuable future (at least not in any way we are aware of in this reality). Taking of a life is inarguably immoral, therefore taking away one's potential to pursue a valuable future is also immoral.
By forcing a woman to carry a child that she does not wish to carry inflicts great harm upon her. She often is left with no choice but to drop out of school or leave her job in order to properly carry, birth and raise the child. Her right to the pursuit of happiness, of becoming educated and working a satisfactory job that also provides income, is taken away.
The sperm and egg that have the potential to become a human cannot be harmed by contraception in any way comparable to the harm that is done to the forced-to-be mother. The sperm and egg, the zygote and the fetus in early stages of development do not have a brain.
To this day, we are only aware of a mind being of existence when firing occurs in the neurons of a brain. To force a woman to have an unwanted pregnancy is to put objects with no mental capacity or thought above a human that will be deeply, negatively affected.
It is true that every egg and sperm have the potential to become a human, contraception decreases this potential. Likewise, ejaculating sperm anywhere but inside of a vagina decreases the potential of creating a new human life. To say that the use of contraception is immoral is also to say that any ejaculation not inside a vagina is immoral. Additionally, it would then follow that having a menstrual period is immoral.