The abortion issue in the US focuses on when and why it might be okay to terminate an abortion. This is a moral issue with legal implications.
Most conservatives oppose abortion, except in the cases of rape, incest, and a danger to the woman's health, and many liberals support abortions in most or all cases (even sometimes including partial birth abortions). Libertarians are divided on the abortion issue, with some believing it is government's duty to protect the unborn (namely organizations such as Libertarians for Life) and some believing that government should meddle into the woman's personal life.
Medicine is designed and justified on the basis of saving and promoting life; abortion does the opposite. A medical professional is ethically bound to help life, and not take a life in the name of maximizing profits or advancing an anti-life agenda. Medical schools are funded with the stated purpose of helping life, not hindering it.
It is unethical for a medical professional -- or anyone else -- to take away life through abortion. It would be unethical for the government to put one group of citizen’s pursuit of happiness over another group's right to be alive. People would be appalled at the immorality, at the disregard for life. And yet this is exactly what is happening.