There's nothing handwavy about the liquidity argument. Improving liquidity reduces the cost of trading for almost everyone in the market and thus makes almost everyone just a little wealthier. That means ordinary people, like schoolteachers and custodians, retire with a bit more money, and are a bit more comfortable; it means lots of people can donate just a bit more money to charitable causes without crossing whatever financial safety line they have, &c.
It's hard to make the same kind of argument about adtech.
It's hard to make the same kind of argument about adtech.