To be specific, on February 25, 2020, Sen. Harris voted against the Born-Alive Abortion Survivors Protection Act, a bill that would “prohibit a health care practitioner from failing to exercise the proper degree of care in the case of a child who survives an abortion or attempted abortion.” That’s called infanticide.

But you don't know that she supports infanticide. Because you don't know why she voted against it. That bill - like most bills, and almost all messaging bills - contains lots of things that people who support abortion rights would vote against in almost every circumstance.

As an example - I know from past conversations that you are against abortion. If I introduced a bill into Congress that included a provision that required every state to allow abortions under the same terms as Roe v. Wade, and included a provision that made it a federal crime to murder puppies, you'd vote against that bill. Does that mean you support murdering puppies? Of course not - you voted against the bill for a different reason.

For this bill, the problem is writing into the statute a definition of "abortion" that describes it as "intentionally kill[ing] the unborn child of a woman known to be pregnant." Any person who supports abortion rights, but opposes infanticide, would vote against the bill for that reason alone.

congress.gov - Senate bill

Which is why nearly every Democrat always votes against this bill in every Congress it comes up (it failed again this Congress). Not because every Democrat supports infanticide - which you must know is false. Because the bill would jeopardize all access to abortion by defining it this way.