If you believe most people on the left, and Planned Parenthood in particular, "a person" isn't really "a person" until they've been completely removed from their mother's womb and the cord has been cut. Up until that moment, and perhaps even beyond, they're "an unviable tissue mass." Pro-abortion dogma states that they're nothing more than a clump of cells. They're not alive, so there's no "death" involved in ending a pregnancy.
This has become a sort of third rail for Democrats. During the last election, both Hillary Clinton and Bernie Sanders refused to utter support for any restrictions on abortion - and any moderate Dem who does will either find themselves shouted-down or run out of the party. Remember, the DNC has made it clear there's "no place" for pro-life (or even anti-late-term) members.