Facebook has definitely undermined trust on what data it shares.
However that is not it’s normal model.
For example Telegram has a very specific approach to security based on "you can trust us", by default chats are not end-to-end encrypted, they use non-standard encryption and the app is free, but they are upfront on why such tradeoffs are made and their point of view in making them.
Facebook could have a position of "personalized advertising is the future" and allow ipertargeted marketing by means of gathering every scrap of data they could find. But they could draw the line to keeping it within their own databases and never distributing any of it. Apparently their main line of bussiness is exactly like that, but they do not do only that, they also partake in sharing that data.
You certainly say they exploit it on behalf of their customers, but we need to maintain the distinction between this, and the companies that actually do sell the data they collect, because once sold, you can never trace who is using the data, whereas with Facebook and Google’s model, you can.
It’s also worth pointing out that it’s not in Facebook’s interest to sell the data. If they did, they would lose their advantage quite quickly.