This man is unfortunately correct. It's not even about the red strikethroughs, it's that there are a lot of users on various websites who only start making passionate arguments about free speech and slippery slopes when the banning of pornography, particularly lolicon, comes up.
Are the arguments they use somewhat technically plausible? Maybe to some. The problem is that on a basic social instinct level it looks really bad when there is a noticeable pattern of behavior with a specific conversational trigger. These types destroy the credibility of their own side if this is detected, and then also the credibility of people who make the same argument with purer motives.
It's simply the reality of it. People who make the kinds of arguments this poster is referencing just do not have a media apparatus suppressing every negative thing they do like the LGBTQ+. They make themselves and others look bad.