Sure, but free is the defect state in the Prisoner's Dilemma. If Google provides a paid option, they'll still be competing with their free option. If they switch entirely to paid, Bing immediately starts advertising as "the free search engine".
This dynamic is even more powerful for network-effects-driven platforms like Twitter or fb
Sure, but the premise was that it would go away if you took away ads as a funding model. I doubt that FB would simply fold and say "oh well" if, by some miraculous law, ads were no longer an option for funding. And Youtube (which is counted as social media here) already has Youtube Premium/Red, where people (at least in some countries) can pay to get an ad-free experience and some extra content.
When people perceive a value, they'll pay an appropriate price in some way (be it by spending money or watching ads), that's all I'm saying. And they appear to value social media or they wouldn't spend that much time on it. So if you remove "just watch some ads" as a payment form, I'm pretty sure that at least some will switch to handing over money.
