As a former member of a union, I honestly find it odd at how many people think that unions are always good. Of the two unions I was a part of and watching what my dad went through with his Union I'm actually fairly anti-union at this point in my life. I watched a guy get fired for sexual harassment, and rehired due to pressure from the Union. I watched my father not get a manager position, because of seniority ruling…
What industry were / are you in? I'd really like to hear about this from people in blue-collar jobs, with small incomes, and smaller bargaining power. I am not sure if a Silicon Valley perspective about this is necessarily representative or useful.
While Silicon Valley may be unique, that just means the things workers in those jobs want to focus their collective bargaining around may be unique, too. Not working in Silicon Valley, I won't pretend to know what those things are, but I certainly know that every workplace has issues and that without unions, the power structure is completely unbalanced in favor of management.
OP mentions sexual harassment. But if the workers wanted, they could actually collectively bargain even STRONGER sexual harassment policies than management wanted!