It is not a contradiction to support both the right to choose abortion but not the death penalty. If you believe you shouldn't kill persons without adequate moral justification, then you may support abortion because you think that fetuses aren't really persons. That is, you may think that a fetus really hasn't started its life, and therefore has no life to lose. But you may oppose the death penalty, because capital criminals have fully developed brains and know they are losing their lives. Many Democrats accept these two positions.
It can go the other way, too. Someone can believe in the death penalty because they think capital criminals deserve it. But they may also think that the fetus is a real person whose right to life has to be respected. Many Republicans are in this boat.
You may disagree with these pairs of positions, but the people who advocate them are not contradicting themselves. The death penalty issue and the abortion issue are two different questions that have to be assessed on their own merits.