In the 19th century, most corporations operated in trusts and cartels, making it difficult for workers to get a fair deal without forming cartels of their own (unions). Most of the violent struggle labor proponents go on about was during this era, when monopolistic trusts would have hired guns (Pinkertons) to suppress labor disputes, and unions in response developed a tendency towards mob violence of their own.

By the 20th century, progressives had enshrined many labor protections into law and broken up the trusts. Some industrialists, like Henry Ford, unilaterally increased wages to inspire worker loyalty and poach the best workers from his competitors. This is perhaps the most analogous situation to the tech boom we see today, and it's this stage in history that pg writes about. Yet despite their gains, unions not only continued operating as cartels but even, in many cases, continued their violent tendencies and developed corruption and ties to organized crime.

Today we have a situation where labor unions have achieved absolute control of certain sectors (longshoremen, teachers, police, Hollywood, airline pilots). The results vary, but are pretty bad for everyone except whoever runs the union. Senior airline pilots manage to capture all the profits generated by the airline while pushing all of the risks onto stockholders, leading to a bankruptcy cycle. (http://philip.greenspun.com/flying/unions-and-airlines). Longshoremen's unions control the assignment of work, erecting a barrier to entry for prospective longshoremen. Hollywood guilds are satisfied by simply rent-seeking. Teachers unions establish themselves in the public eye as credible authorities on education rather than simply a labor union seeking better terms for its members. (Rhetoric about standardized testing can't be taken at face value--notice how often you hear that a teacher's subjective judgment of student performance is more reliable than a standardized measurement. What the NEA really fears is any system that can measure the performance of teachers rather than simply trusting them implicitly once they have their union card.) Police unions--well, you tell me why shooting a black kid in cold blood gets a cop paid suspension and anyone else criminal charges.

In most cases, unions will resist automation, resist any measurement of performance in favor of seniority, and otherwise impede the efficient operation of their employers. And in many cases, they don't even help the median worker all that much. Once a union has a closed shop, the tendency to reward seniority will metastasize until the union shits on junior pilots and "casual" longshoremen more than management would have done in the first place.

And this is why people who support unions will tell you all about what unions did a hundred years ago, because what they're doing now is not a very pretty story.

(Note: I'm referring chiefly to American unions. In Germany, unions have seats on the board of directors and presumably also stock in the companies their members work for. This presumably tempers the parasitic tendencies American unions have developed. It's worth noting that UAW vehemently resisted having to hold stock in GM as a condition of the government bailing them out of GM's insolvency.)