The people who are anti union have probably never worked in a big company that without a union presence , would be still working for award wages for doing work that the average joe blow wouldn't want to do.
For the self employed.....that's a choice you make, so unions are not your problem.
I've worked for fairly big wages ( under union rule ) and now work for award wages at a factory.....nearly $80,000 difference, but for workplace safety ( which hopefully keeps you alive ) I'd take the union place any day..
If you look at the safety record of union controlled companies compared to the same type companies with no unions ( USA coal mines is but one ), you may understand that unions do have a place ..
I've worked in union and non-unionised environments (youth work in the UK), and would much prefer the unionised environment for the following reason:
1) The feeling that you have people to back you up, and not hang you out to dry
2) The support that you get from your membership (for example, legal services for all immediate family... not one of those you ever want to use, but when you have the backing of the legal services of one of the biggest UK unions, it's nice knowing it's there!)
3) Transparent pay scales and structures, with clearly defined role expectations and acting up pay when people act up.
However, I also fear that they are their own worst enemies because:
1) The unionised pay scales prevent market relevant pay (and therefore leads to the need for keyworker housing etc to enable those workers to live in the major cities/South East - my £30,000 pay was great in Blackpool, but wouldn't have been as good in Berkshire where I grew up). It also removes in Australia any cost savings to relocate operations out of the major cities - Why would I move my Western Sydney manufacturing operation which pays Award Wages to a regional Area where I'd still pay Award wages... it would cost the business to move, whilst potentially being advantageous to the workers in the short term
2) The union will sometimes have "interesting" personalities in it who will (deliberately) look for the rope to make the noose for the manager
Overall, I recommend unions in any environment where there are threats to your safety in your workplace (retail, extractive industries, construction etc), management can change the conditions you are working under (roster, wages, hours etc) or where you at risk of management's decisions coming back to bite you on your arse, whilst they get away scot free.