How can liberals claim our founding documents protect abortion rights?

Thomas Jefferson spoke about unalienable rights being LIFE, LIBERTY, and the PURSUIT OF HAPPINESS. Why do liberals ignore the baby/fetus's right to life? They'll back the anti death penalty movement while backing the killing of the unborn. Explain this please! Conservatives back the death penalty to those who took the life of others in most cases, so don't claim this to be a contradiction please. Unborn children did nothing wrong, convicted criminals did!