I wrote in another post which I think fits nicely here: You are ignoring things like lockup periods, vesting schedules, and other general machinery that specifically exist to prevent day 1 or short-term dumps of shares. It's not in the interest of the company that is IPOing or the bank - how can the investment bank go to investors and market securities and then on Day 1 those securities (because it's a pump and dump remember?) drop by 10% - 20% - 30% or more. That's bad business and investors will leave investment firms that did that.

> Retail investors are the marks, not the scammer here.

Retail investors who aren't sophisticated enough to do analysis and evaluate equities shouldn't buy them less they potentially lose (or make) money. You're inventing a scam and scammers where none exist here. Uninformed retail investors, and who knows how much money they even have, should be buying index funds which is what is advised by investment firms, CFPs, and more.