There was no argument to defend to, only a misconception to correct.
But, if you really want to make the argument that "we shouldn't fill the catacombs", then feel free to petition the IGC, because it is "they", not "we", who are in charge. Be more precise in your petition, though, because "the catacombs" is a very specific and profitable part of the system that no one ever thought of filling up with anything but tourists.
FWIW, I haven't gone down there for nearly three decades so I don't care one bit about the catacombs and the cataphiles. While I have very fond memories of the time I spent down there when I was younger, I moved on, as most people did. If "they" need to fill up a short section somewhere to prevent collapse during the new Metro works, I am fine with it.