There are pros and cons to unionization, but imo not all workers should unionize. Most of my hardcore union friends think I'm "anti union", even though I think some workers should unionize for their own good (I'm looking at you, non-tenured college professors.)
I come from a union town. My grandfather was a union organizer and disowned his sister for crossing a picket line. My mother worked in a union her whole life. My father was a union steward, then halfway through his career entered management and had grievances filed against him. I was - briefly - a dues-paying member of a union as a teenager (IBEW) for my summer job. I have many friends in trade unions (plumbing, electrician, etc.) and I have friends in SAG.
The relatively high standard of living I enjoyed as a child was in large part the result of my parents being in unions.
Sure, mom had to sometimes see less skilled co-workers get promoted before her due to seniority, but she wouldn't have had the good pay, benefits, or job security without the union. That's the trade-off, and for her it was worth it in the long run.
However, the downside of a union encouraging low productivity can be very real.
Case in point - where my father worked, the union was so entrenched that the high seniority factory workers were making as much as local software developers (nothing necessarily wrong with that), but their productivity was far below workers doing the same job in a non-unionized factory being paid far less in another state. When they were asked to increase productivity to meet that level, they balked. For years. Then went on strike. And as a result, at least partly, that business was sold off and a lot of them were laid off.
It's always a set of trade-offs but I think plug-and-play workers should organize. They need to be able to collectively bargain. They just don't have the same individual leverage like say, software developers.
The problem is that we're not in the heyday of unionization anymore. Few industries are unionized nationwide, so companies can just move to another state. Unions don't have the leverage they used to, so organizing can end up being a footgun. That might mean that business has too much of an advantage, not that unionization is bad, but it depends on your worldview. But without unions, it's just always going to be a race to the bottom for unskilled labor. How could it not be?
Trade unions and guilds (like SAG) are a totally different animal.
SAG is great because you work for an ephemeral production, not a company. Game development should definitely adopt this model, because games are really just movies now. You get your benefits through the union when you're not actively working, etc. Not a bad deal, and probably better for the production companies.
Trade unions - they restrict the supply of labor, driving prices up, but they police themselves and maintain quality. I would be uncomfortable hiring a non-union plumber for anything non-trivial.
Anyways, like I said, it's all a set of trade-offs, and those vary depending on the industry.