When workers organize and attempt to make demands greater than than the bosses are willing accede to, the bosses call in the police, private security, and depending on the political climate, right wing street fighters to start cracking heads. For a famous example of a dual power situation consider the 1934 Minneapolis teamsters' strike.
Even setting aside the obvious "Two wrongs do not make a right" response, if you have to cite history from 3/4 of a century ago, well...good luck persuading people with that. On the other hand, the public can easily find news stories of major corruption and criminal involvement by unions for each of the past few decades.
(Oh, and by the way, the Teamsters, whose site you linked to, figure prominently in quite a number of those news stories. There really isn't a better example I can think of of why "Workers need to be willing to break the law in order to win victories against the people that make the laws..." goes down a bad path than them. The Wikipedia article for them contains the word "corrupt" 31 times.)
https://teamster.org/about/teamster-history/1934