No one will trust them again if they make one major mistake, and Ads are a minefield for upcoming regulations.
They have so much money and financing available, instead of being greedy, they should focus on hardware.
Now, I do agree that it is a systemic risk to the company. Ultimately, businesses/people/organizations respond to incentives, and for businesses that is usually revenue. If your revenue comes from your customers, you're more likely to be aligned to the needs of your customers and try to meet their needs.
However, with advertising, your customer is the advertiser, not the end-user. Additionally, your end user probably doesn't want advertising, so your incentives are now significantly misaligned with your end-user. Maybe that is fine for the near term, but each small decision that's pro-advertiser and anti-user compounds over time and eventually, creates a more user-hostile product.
Also, as an aside, I expect the stock price drives decisions way more than how much money Apple has in reserve.