The difference, like many things in traditional finance and cryptocurrency, is disclosure.

The activities of the market makers are well disclosed in a comprehensive IPO disclosure document. Importantly, any relationship between the underwriters and the company they are underwriting is well disclosed.

Meanwhile, folks tout the transparency of the public ledger, but actually the transparency is very shallow and disclosure is very poor, particularly around conflicts of interest.

Additionally, if the company lies to make the "pump" you can put the shares back to the company (per the securities act).

You just have to look at what happened to WeWork to see the IPO disclosure process successfully killing a bad company.

Beyond that point (is it necessary?) an IPO in the US is heavily regulated, disclosure by the SEC, underwriter activities by FINRA and the listing itself by the stock exchange.

I don't think you can call IPO market support "pump and dump".

Don’t banks put a fair amount of work into evaluating the valuation of these companies whose equities they are putting out on the public market the first time? The company is putting their trust in the bank that the banks valuation isn’t too far off from what the market would think. There have been botched ipos where the price of the ipo was too high and the stock sunk like a rock, and also where they were too low and the company didn’t make as much on the offering as they could have. Don’t ask me how its done, because banks are the experts at these valuations (some combination of math and convincing the right group of people they want to get in on the offering at a given price) and thats why companies work with them on ipos :)

If the bank buys a share from someone else without any arrangement they are taking a risk. Their motive may be to support the price but people buy and sell shares with all sorts of motives.

If you buy a share from your self or from a party where you have an agreement to trade back at a fix price, no risk is taken. That's called a "wash trade" and is illegal for securities.