In cases where labor is less like a commodity and/or when the employee, customer and employer lines are blurry (as is the case with city and town employees but less so with say, the IRS) there is less benefit to unionization.
I do think that unions would be a net positive for most gig-economy workers though.
I remembering reading a foreword to Animal Farm, saying how Orwell was able to predict the dystopian aspects of technology, but wasn't able to see how technology could bring about social change for the good (like the shortwave being used to communicate across borders and into dictatorships).
I think this type of statement shows just how much we miss this currently when we bemoan every tech dark side.
The same decentralized tech aspect of Uber that helped change the ride service industry, can also help the drivers fight being exploited.
My theory, very weakly held, is that many in our industry are naturally pessimistic (I know I am) and it helps us see all of the ways that things can go wrong and help us prevent them. But I think we're also missing out on a lot of opportunities that would help use the same tech to counter the outcomes.
It's like fire. We can burn the world, hurt each other, and tear down society. But we can use it to warm the world, help each other and build society. Both are kind of inevitable.
See: Facebook, Google, Amazon.