> paper / magazine ads add a few grams of weight and a bit of volume, but rarely in noticeable amounts
Have you even seen dead-tree magazines in the lase ~decade? They are often half (or more!) ads. I hardly call >50% of the volume/mass to be "rarely noticeable".
I'm sure there are counterexamples of saner magazines, but they are certainly not the common experience.
Computer ads aren't free for the people subjected to them, since we're the ones that have to do the work of displaying them. Compare that to paper / magazine ads add a few grams of weight and a bit of volume, but rarely in noticeable amounts, and billboard ads that don't cost the recipient any resources by being there (except maybe having to step around them).