I am watching a certain show at the moment where someone is talking about wanting to kill evil creatures. Please don't judge this question as childish just because the extract is from an anime.
He says
くちくしてやる。この世から。一匹残らず
I understand that, but then he says
もっとだ。もっと。もっと殺したい。
I don't understand why he would say もっとだ. The reason why is that I don't know what he is saying exists as 「もっと...」, if you understand what I mean. I know the meaning of the word, I just don't get why he would say だ afterwards. Like, if I asked in Japanese I would say... 何が「もっと」ですか? What would replace 何 in that question?
Is だ just emphasis of how much he wants to kill more?