Perhaps it’s not the best example. Replace it with something more specific if you wish, like “placing live fragmentation grenades in one’s mouth in moderation”.
“Moderate use of porn” doesn’t have to mean hardcore pornography. Playboy and erotic novels are probably not equivalent to Anal Whores 3.
Similarly, I’ve also heard the argument that high-speed internet pornography and “tube” sites in particular are the problem, because of how they present to the user a never-ending stream of novelty, and not necessarily because of the particular type of content.
If that’s the case then obviously the argument about moderation would have its merits.
It's possible to become addicted to much softer varieties of porn, but the potential ramifications of that addiction may be less severe (or they might be problematic in another sense, like financially).
For example an extension that tracks your porn viewing habits and limits video recommendations.
IOW “if X is in moderation, X is fine” is logically consistent with “some things cannot be in moderation”.