First, I take great exception to your statement that “all Google employees who are Muslim or Christian [...] find themselves [...] working for a company that has an official position [...] that is strongly against their own.” A huge number of Christians or Muslims oppose proposition 8, and to suggest that all members of certain religion groups favor the proposition is, at best, strongly misinformed.

Second, I don’t see how you can reasonably claim that Brin is “impos[ing] his views on all of his workforce”. I’ll not deny that some of his workers might disagree with his views, but I don’t see any imposition taking place–He’s not forcing them to agree with his views, to promote them on behalf of the company, or otherwise forcing them to take any action at all that violates their personal conscience.

Third, I think you’re off base when you suggest that the head of a company is answerable to his employees when it comes to taking political stances. Brin has no responsibility to his employees in that regard–Instead, he’s responsible to the shareholders. And Google shareholders overwhelmingly support his position (mostly of course, because Google shareholders are overwhelmingly Brin and Page)

The question of whether corporations can take a position on the questions you raise is long settled and the answer is yes. You specifically cite the example of supporting a presidential candidate. Candidates for many offices, including US president, have long sought and received support from both companies and unions.

As to power over content, Google cannot avoid it. No content provider on the net, radio, television, newspaper, or whatever can avoid it. They have content and the value they bring to the world is that they present the content in a sequence and a format that they find valuable. Their sequencing of one thing ahead of another is the power to make one thing more prominent than another in a particular context. Absent the ability to present everything on a subject at exactly the same time in exactly the same way, they must choose. You call it power to promote a view, which is true, but incomplete unless you also realize that they lack the power to do otherwise. The question is where to draw the line. The answer is that the line has long since been drawn and he is pretty far from crossing it.