The best HN commenters come here for the opportunity to contribute something far better than that, and we all benefit when they do.
A company that clearly aspires to control the communications system that global society increasingly relies on for everything, that spends massive amounts to influence governments, that controls the visibility and economic destiny of the journalistic organizations that might hold them accountable... could decide to, ya know, do a lot of bad stuff?
For all X, there is a path from X to great harm. Likeliness is critically important in evaluating whether X is still a good thing or not. I grant that your scenario is possible, but I consider it very unlikely.
Wasn't that the entire premise of embrace, extend, extinguish? Sure, adopting open source technology is good, but it seems to me that Google's in the "extend" phase rather than being actually altruistic.
Android is not entirely open-source. Chrome browser is not entirely open-source. Google Web Apps are not open source. Google Search is not open source.