If IPO pop was something nefarious, how do you explain IPO pop of Goldman Sachs stock? They ran their own IPO and you can be sure as hell that partners didn't want to leave any money on the table.
In general, IPO pop is an interesting phenomenon and it's not fully explained in the literature.
The optimal return for partners probably is giving the institutional investors a pop on even your own IPO so you keep them as investors for future IPOs where you are collecting fees. When the institutional investors lose money on an IPO, are they going to come back to you for the next one?
Yes, in an ideal world you "price it right" and on IPO day the stock doesnt move up or down from the opening price.
Optically, it looks a lot better to price low and have the stock rise.
Additionally, there is something called an over-allotment option (aka greenshoe) that allows banks to sell more shares than initially allotted, to help stabilize the IPO price. This is usually more $ for the banks.