You can't simplify the issue down to there being one action that is more profitable and one that is less so. the world is more complicated than that. Forgoing some profit in the short term in order to gain some trust from the userbase may be more profitable in the long run. Or maybe it won't be. It's a decision that facebook's leadership has to make, and it's not as simple as "we'll take the option that makes more money".
Burning down my house would net me a nice payout from the insurance company, but it's probably not a good financial decision in the longer term. when looking at corporate motivations, it's easy to say they're going to pick the most evil choice if it's the profitable one, but business leaders aren't all stupid, and picking the evil choice is often stupid.
it's pretty hard to find a business decision that can be reduced down to "should we make money, or not make money?"