Anyone can look up a co-worker's salary from data made available by the tax office. (Of course the information is about a year out of date because it's based on tax returns.)
Are employees "reduced to numbers" in Sweden and Finland? Certainly not. On the contrary, these societies are considered some of the most open and equal in the world. Maybe salary transparency has something to do with it too.
decent pay, but not much incentive to strive for more
Isn't that a good thing? I mean striving for more based on intrinsic motivation than financial. My observation in over the past 12 years working in the software industry is that bad motivation (both carrot and stick) tend to drive out the good (desire to build something or solve a problem).You're assuming that this model, where pay is determined by how well you banter when you sign up, is the only possible one. This model is entirely manufactured by employers to let them fleece employees, and they make rules to forbid discussing your salary precisely to keep employees from realizing how bullshit it is.
In a transparent salary environment, the management is incentivized to pay everyone equitably based on their actual value to avoid the "OMG Susie gets paid 40% more than I do for exactly the same job" problem.
Which means management is incentivized to probably pay mediocre employees a little more, and stand-out employees less than they could have otherwise earned.
Unionizing creative industries (I'm including most of software development here, as it's what I do) would serve to put a big safety blanket around the tons of mediocre talent there is out there, makes it harder to fire poor talent, and make all of our overhead higher (i.e. software costs more or profit margins are much smaller, both a bad thing for bootstrapping new products) without much overall boost to productivity or talent in the industry.
Mediocre/poor talent wins, everyone else loses. Doesn't sound particularly attractive from either side of the coin.