GIGO.
Google is trying to pass this incident as a hallucination but it isn't.
It is a proper response, based on its inputs, exposing a rarely reported current in academic circles that believes that for the planet to survive, vast numbers of humans must die. It is a modern melding of eugenics, Malthusian demographics, MARCHING MORONS* theory, extremist ecology politics, and elitist sociology. There is vast assortment of screeds online presenting the species as a plague, virus, or infestation. One example being a University of Colorado professor that gained notoriety years ago for suggesting that come a pandemic (this was way before Covid) the governments of the world should do...nothing.
There are thousands if not millions of papers and online posts echoing such thought so the *words* reflecting such ideas have fairly strong links and a LLM that only knows how to process data based on such links will parrot and paraphrase those concepts in response to adjacent queries.
Now, Google's ChatBot is a rush job attempt to keep ChatGPT and its derivatives from undercutting the Google search cash cow. As such it lacks the mind of "guardrail" postprocessing(?) that identifies controversial responses. So it sees no problem in telling a supplicant to eat rocks or kill themselves.
Garbage In, Garbage Out.
Use a broken tool, get back broken answers.
*THE MARCHING MORONS is a Classic Science Fiction story from 1951 to parody Madison Avenue marketing culture using the generally misunderstood demographic factoid that "poor uneducated" people tend to have more children than "smart affluent" people. Mike judge's comedy film IDIOCRACY plays with that story as farce, to good effect. Google's chatbot took it seriously.
(WIKIPEDIA has good entries for both the story and the movie for the interested.)