The SST has an article on young people joining unions. This is actually a pretty sensible thing to do for many young people. I helped several teeangares I knew (they were in my venturer unit) join a union when their employer (a suopermarket owner) was making unreasonable and illegal demands of them. The union was very good as an advocate for them, as it is pretty hard to be assertive of your rights as a 15 year old.
As people get older and more confident, most of them have less of a need for someone else to represent them. Personally there is no substitute for direct communications between an employer and employee, but it does depend on your job and your employer.
Where unions annoy me is where they get overly political and are more worried about the Sandinstas in Nicarargua or sporting tours than actually representing their members direct interests. At least with voluntary membership now people can and do leave if they get too political. However in the state sector the Government/taxpayer bribes employees to become union members so that many people join to get the bribe, but don’t want to be members as they think the union is crap at communicating with them and takes them for granted etc.