To the point at which one is offered real, expert, and/or verifiably backed information contrary to one's position. Then it is no longer necessary to listen to an incorrect opinion. One certainly can be entitled to an opinion, but they are not entitled to the recipient of that opinion accepting it.

Offer the information one time, then let it go. There's an often repeated phrase that "you cannot reason a person out of a position that they did not use reason to get themselves into". There's no point in continuing to engage with someone who has willfully rejected the readily available correct information and actively sought out BS. The facts are out there. What people have taken lifetimes to study, is verifiable in real-world application, craft intelligent and understandable results, checked against peers' work, had peers check their work is the truth until better evidence arrives.

It's a slippery slope if you engage with someone who is loaded with wrong opinion, it's likely all they will do is butwhatabout their opponent. They will not argue in good faith. The opponent will do their best to offer the most correct information they know and decline to offer facts of which they are unsure of; the butwhatabouter will proceed until they encounter a gap in knowledge or fact and pounce, declaring victory, because to them the absence of contrary knowledge is as good as victory.