While it was not quite our first topic, it comes very close, with multiple threads on the first page. Even now, many consider this to be the reason for our founding.
The run-down: Some mothers who didn't want to leave their children at home over the con tried to campaign to be allowed to bring them along, including into screenings. Eventually this morphed into triggerwank and warningwank. See Vividcon and Ableism for details.
First-page threads on babbies at Vividcon:
Also involved were Amadi, who compared being a nursing mother to being a wheelchair user (discussion here); and Ruthi, who argued at some_stars' place that banning babies = “limiting women's freedom of movement.”
Some later threads on babbies at Vividcon in the first meme post: