Abortion opponents do consider abortion as taking a life, sure. I disagree with that, but there's something more pressing--and somewhat disturbing--in your case I want to take up. Abortion historically was permissible until as late as the quickening, and many major religions have nuanced, diverse, and conflicting views on the issue, within the religions themselves (1).
Historically, technology for abortion did not exist. However, it existed in another form - infantcide. The two are more closely related than pro-abortionists would claim them to be, as the only difference is that the baby is in the womb and is slightly less developed.
Infantcide was common in the entire world, with its rate being up to 50% in hunter-gatherer or nomadic societies. Civilization reduced its rate, but didn't prevent it. For the case of Europe, infantcide was permitted with no reprecussion under Roman law. Only until the Empire converted to Christianity was there legislation to prohibit the practice and punish partakers.
So, you can thank those Abrahamic faiths for valuing the gift of life as to oppose its unjust violation as the case of abortion.
How can you possibly justify the death penalty for abortion? Murder is different--it is an act more or less universally condemned. Discussions of the DP itself aside (though obviously how you justify use of the DP matters to this discussion, and feel free to add that), abortion is an issue surrounded by extreme moral uncertainty. That is, you cannot possibly know when morally significant life begins, because when it begins is subject to what you argue constitutes morally significant.
It isn't moral uncertainty from the conservative or religious perspective. For they, definitely, declare life to begin at conception. As to why it is a moral uncertainty is due to the devaluation of life caused by secularism - which introduced widespread abortion programs and practices under eugenics programs. Eugenics might be (partially) gone, but socially based abortion is still abortion.
From our perspective, it is the same argument of the 4th century Roman Empire with regards to infantcide. Our opponents may not see abortion as murder, because they justify it as a "moral uncertainty." It is not. Rather, it is a justification to value hedonism of a woman over the value of life. The convenient benefits of abortion delude people to re-define life.
This difference, as I mentioned, is analogous to the Roman-Christian perspective that believed infantcide is a bad thing while the Roman-Pagan perspective believed infantcide to not be an issue as their worldview didn't value life. In other words, pro-abortionists place less value on life than anti-abortionists.
Even defining "life" by itself is a headache and a half. Life as scientifically defined so far can't give a definitive answer; it's a description of things we've observed that signify an individual life, and it faces immense controversy (2). One possible answer is to say that all life is morally significant. Bacteria clearly aren't, so you could refine that to say "all human life". But then we're just begging the question: what is life, and furthermore, what does it mean to be human? Is a clump of human cells "human life"? And if you cede that life does not begin at conception, where can you possibly draw the line? There's a general range of times people believe acceptable--late-term is generally considered life, for instance--but can you pin down the exact point at which abortion stops ending a pregnancy and starts ending a life?
Is a clump of human cells with human organs, a functioning brain, a human-like body, a heart, blood, etc. You can't make the case of "drawing the barrier," because anti-abortionists have drawn the layer with a chisel-thick Sharpie. The barrier is conception.
Based on the view of considering a fetus to be life, and the advocation of the death penalty for murder, I do boldly claim that the punishment for abortion must be death. The only exceptions could include life in danger or rape (even so, a C-section is a potential alternative).
If we consider a fetus to be living and part of life, suddenly - the death penalty for abortion doesn't appear radical or asnine in one bit.