I understand that you work for Google and that not holding this opinion would mean that you have to conclude that your employer is also very much in the wrong. But how do you justify it?
It's clearly not information that people have chosen to give to Facebook. Facebook is basically taking advantage of a technical trick in order to obtain information about their users which their users neither gave them permission to collect, nor know they are collecting. It just seems highly unethical to me. But you "have no problem" with it... How is that possible?
The thing that annoys me about it is that the browser vendors could prevent this hidden tracking quite easily. By either disabling third party cookies, or by tying them to the domain in the address bar. Hell, Safari blocks third party cookies by default, and Apple is all about usability, so it can't cause that many problems... On the other hand, why would Google and Microsoft modify their browsers in such a way as to increase our privacy at the expense of their profit.