As someone who has worked with unions, what you are saying is wrong. Unions in the public image (and their original intention) were to do as you said, protect the workers, Nowadays, unions do everything they can to disrupt workplace environments. Similar to how Trump has appealed to the lowest rung of society and feeds on misinformation, unions do the same. Ive dealt in situations where employees caught stealing (thousands of dollars) and breaking confidentially agreements were protected by the union and wouldnt be allowed to be fired without threatening legal action back against the business. They go to the media, lie about the issues to rile up support and cause damage to the business, yet the business cant speak out about the issue due to confidentiality.
The unions will lie to their members as well. They will rely on mis-information (or lack of information) to their members to first gain unionization. They will make promises (they cant keep) of better wages, hours, benefits, more influence in the business, etc and will go after the employees at the lowest levels (they love people where english isnt their first language). Yet they fail to tell them, these increased wages for many people will not even be enough to cover the union dues. They fail to tell them that this process will take time (ive seen as long as 2 years) and during that time, no raises, no bonuses and no influence in the business. After unionization, you no longer can tell me about an issue, you no longer can provide input on functions in the business. The only thing a manager can say to you, is go tell your union rep. You might think this is wrong/unfair, but any issue that is dealt with, without the unions involvement, the union will sue over (irregardless of the outcome). Unions have become an organization to make money, they no longer act on their original purpose.
Now im not against unions, as long as those unions do what you think they do and not the actions they currently take.