This defense will be relatively easy for Google's leadership to counter. To the extent that it's used, the leadership will be able to say that the unionization effort isn't about working conditions. Instead, it's about political differences (and political differences that are distinct from what almost anyone thinks of as "working conditions").
I could be wrong, but "Google SWEs are unhappy with the leadership's political choices" doesn't sound like a winning rhetorical strategy.
It’s a classic principal agent problem. You want to take the voting power away from those with the financial stake and expect the people without a financial mistake to make good business decisions.
I'd say the second criteria is infinitely more useful, and empirically it works. The most stable bank in North America is democratically run by both customers and employees, I'm a very happy customer, and I know of many happy employees.
The truth is, many Google software engineers are unhappy with the political choices that Google are making. Yeah, they could vote with their feet and quit, but would you take a massive pay cut and financially destabilize your family as the first course of action? I wouldn't; I'd try to exact change from within, whilst protecting the benefits I'd earned in the workplace.
And all that's just looking at the individuals benefits. Unionising would mean that I, a straight white man, could help support policies that empower my minority co-workers.