I belong to a union. I got nothing but good things to say about my union and it's members. On more than one occasion the union has been there for me and my family.
Most unions expect you to gain employment first before they accept you as a member. Most of the time jobs are found through the "Good Ol' Boy" network but I once walked into a job site and was hired on the spot and got into the Service Employees Union in New York City. From there I networked and managed to get a job working HVAC and got into their union.
Most union's offer Pensions and Annuity's. They also offer low cost health coverage upon retirement.
I get that they are not as powerful as they once were but they are evolving. At least the one i belong to is, with training and education in the field our members are in; which is an incentive for employers to keep us on the job.
I've been in a union. They helped me out when my bosses were making me work for less than my job position paid. They also tried to make me do two jobs for the price of one. I believe the union people kept management from treating us like dogs. You know, it was hard to part with my union dues, but I was glad I did. And, at this job, getting support from the union didn't hold back my career development because the managers had learned to accept the union as a 'necessary evil.'
At my last position, I was bullied to skip breaks and do homework and it became a huge problem between me and my boss. If there had been a union at this position, my boss would never have had the balls to try that crap.
I would join a union just for the protection from management.