That is who they are.
If any Leftist did speak out to say they were offended or disgusted by that little piece of theater, one might reasonably see this conversation:
PRO-ABORTION PROTESTER: What that person did there was disgusting. That isn't what we are protesting about.
PRO-LIFE OBSERVER: Really? Explain to me how what we saw in that video is more offensive than what is really done to a full-term baby in the process of aborting it?
PRO-ABORTION PROTESTER: Look. We aren't drinking the blood of the bab-er, fetus, or eating it, either.
PRO-LIFE OBSERVER: Maybe so, but you are certainly celebrating it. Your "protests" are full of people who seem absolutely joyous over the concept of killing a fully formed human baby. And don't bother denying that, we have video of it, a lot of it.
PRO-ABORTION PROTESTER: It isn't the same. That person is showing it being cut out with a butcher knife and ripped from the womb.
PRO-LIFE OBSERVER: And how is that different from having a steel tube inserted into the baby's skull, sucking out its brains, and dismembering it, which is how a real late-term abortion is done?