Your comment reads like Apple removed the ability of Facebook to monetize apps with advertising (which they didn't), and reads as if tracking users' every movement is the only way to advertise (which it isn't).

Furthermore, there are plenty of unjust/unethical systems in this world that - if dismantled - would cost the jobs of honest, hardworking people. That doesn't seem like a valid argument against the question of whether or not tracking people without their consent is itself unethical.

Edit: I want to bring up another point: You mention that using FB ads can allow developers to avoid the "Apple Tax." But not only does the Facebook Audience Network apply its own tax (via revenue share) to app developers, it also refuses to disclose that number! So if you monetize a free app with Facebook, you're paying an undisclosed Facebook tax. Given the Google tax for AdSense is 32%, it's likely that FB's secret tax is higher.