Some industries. You can reliably justify unionization.

Industrial Work can be hot, dangerous, and expose workers to health problems. A Union may be justified there.

Teaching?. You deal with kids all day and can reasonably work literally everywhere in the country. You get to be an air conditioned classroom. And barring the inner city schools. Your Job is comparatively safer then most others. A Union doesn’t particularly serve a purpose. Other then to squeeze more money for paychecks out of a City or School District. That and prevent shit teachers from being fired.

The amount of shit the Teachers Union’s get brushed under the rug is frankly disturbing.