If they consider allowing women to get abortions infanticide, I can see where they're coming from. From another perspective, if they consider donating weapons to Israel to help them kill Gazans, including children, infanticide, that would also be something that many Democrats support.
Edit: I didn't say my own opinions on either of these being infanticide, or at least immoral. I was just trying to understand it from various points of view, to see what they could have meant.