It's a fair assumption that the majority of the code on the internet probably isn't written by you, so what you or any other individual writes isn't exactly a counter-argument.
I'd assume the poster you replied to was referring to the Javascript that gets delivered to their browser on a day to day basis by general purpose web sites, for which a significant percentage being ads and related unwanted content is entirely plausible.
If you were to capture all of the Javascript delivered to a randomly selected person's browser during a normal day I would easily believe somewhere between 50 and 80 percent of that Javascript was things that if the user was given a real choice they would not choose to load.