That is after the baby is born and is therefore the responsibility of both parents. This I wholeheartedly agree is 50% both the father and mother's rights. However, as long as the embryo/fetus is housed in the mother taking her resources and burdening her, she has most if not all the rights to the embryo.
It does not have to be. Once the baby is born, if the mother doesn't want it, she can remove herself from the picture. Maybe pay some child support because, after all, a father still has to pay child support if he didn't want the child and the mother went through with the pregnancy.
It's also not as though the father is unburdened by the pregnancy. When a woman is pregnant, she cannot work and exert herself the same way she can when she isn't pregnant, hence why maternity leave is a thing during pregnancies. The father then provides support and aid to the mother, who cannot do so for herself after a certain point.
You also cannot ignore that 18 years of physical, mental, financial, and emotional exertion to support a growing child and yourself isn't more exertion than 8 months of pregnancy. You can say that the father isn't as exerted DURING pregnancy, but raising a child requires FAR more exertion than housing a child during pregnancy if not for the far more intense time span. Then there is also teaching the child, making sure the child is educated, making sure the child is disciplined, etc., which can all be broken into more and more tasks. You're laughably wrong if you think a pregnancy is as hard as raising a child. Difficult? You bet your ass its damn difficult, but not more difficult.