Just take ad revenues (not just gross profits since we also want to count the money going to publishers) of large tech firms. Then deduct however much of that y

Just take ad revenues (not just gross profits since we also want to count the money going to publishers) of large tech firms. Then deduct however much of that you think was the reduction in offline advertising (most of it, non personalized) as ad spend shifted to online. Then add another 20-50% of typical ROI (an advertiser would only spend $1 on ads if they think it would increase their profits by $1.20-$1.50). You would easily arrive at the ballpark of several hundred billion. If you disallow sites from using third party ads and ad tech, they would only get a small fraction of their normal ad revenues. Even without that, many publishers end up giving up on the ad model, either going for paid content / promos (far more misleading IMO), subscriptions, transactions, or just shut down entirely. If you reduce ad income by several times, a lot of free stuff on the web will disappear, and with it the jobs at those publishers and the advertisers who sell more things due to those ads (non personalized ads aren't very effective). I'm not saying it's bad, I'm just saying that's something worth knowing before settling on an opinion about this topic.