It's more than that. The 10% is the scam ads that "won" the ad auctions. It doesn't include the effect of scam ads bidding up the market and increasing the price of non-scam ad wins.

(Could also argue that the scam ad that won the slot for 10 cents would have gone for 9 cents without the scam and Meta's marginal revenue was only 1 cent... but if every ad is 1 cent more...)

Same problem when you want to buy a home in a place where real estate became a means for money laundering or uninhabited store of value