Interesting conversation you have.
My opinion has no importance, i'm not american citizen and i'm not a professionnal arborist. But i feel i got to tell a little as i used to be an employee representant in an union, as a future recreational tree climbing instructor i will have to get into our national union of tree climbing instructors. and my girlfriend is responsable of an union into national monuments.
My first experience was into the CFDT, a global union represented in allmost every professions, the biggest french union in fact.
It appears that the main job of the CFDT is to say to employees that it is there to protect them and to prove to employers that they don't give a damn about employees... it is a corrupted union where responsables are using of their strategic fonction to get promoted. I came into it because they asked me to, i was curious and i thought it could be good to solve troubles we had in our department. Since the first reunion i learned by facts that i wasn't allowed by my "camrads" to ask the questions needed to be asked. Our problems were big, really big, it was a security matter and the employer was breacking the law on 7 different points. It tooked me 2 years before i'd been able to ask my questions... through an other union !
My second one will come soon with the SNGEA, national union of recreational tree climbers, yes it exists ^^
Being member of this union offers several benefits. First we have access to a good professionnal insurance covering our activity, for instructors but also for their students. For something like 160$ a year we are fully covered. That's really interesting. Other benefit is that thanks to this union we are recognize by our government and so we have in France the first (and so far as i know the only) diploma of TC instructors recognized by a state. Wich is a big thing because in France it is just impossible to be paid for a sportive instruction if you don't have a state diploma. Without the SNGEA we couldn't live of recreationnal TC, only the rock climbing instructors could do it even if they are absolutly not specialised in TC. Bad side is that the SNGEA is a bit monopolising how the profession evolves and sometime it appears that it creates a lack of creativity, but that's not a big deal.
I can also witness how it goes for my girlfriend. We have huge troubles in culture development and in historical monuments management. She started to be envolved during a wave of agent depressions and even suicides because of work conditions, i guess it is enough to explain how bad it goes without having to detail all troubles you can find in this management. Government is in charge through the ministry of culture and here (i guess in other country too...) the biggest law breaker is the one that creates and apply laws. Her union is the CGT, the second biggest one in France after the CFDT. The CGT also had troubles of corruption and employees manipulation, but in her section they do an amazing job. They obtained to get fired responsables (that never happen before their fight) that were harassing employees, provocating depressions and suicides, some other are still in charge but they know that there are limits they can't cross now. With her camrads she still fight on many difficult subjects, and she has the power to meet highest reponsables in charge, a week ago she was giving in person a letter of grievance to our new minister of culture.
To me it looks that unions have good sides and bad sides. Consequences can be pretty big because unions can be really powerfull. But there are no particular good or bad sides allways correlative to unions. If an union exist but doesn't make anything there wont be no good or wrong consequences because of the union. Unions are just made of people. And that's only the qualities of people that brings positive or negative consequences. Put together a bunch of corrupted lyers and you'll get a toxic union, put together great upright people and you'll get a great effective union. Put together both of them, as it is allmost every time the case, and you'll get a mess sometime doing good, sometime doing wrong...
But it is absolutly sure that if you let employers, shareholders, governments etc, do whatever they want without the pressure of people you'll be screwed to the bones so often.
So to me the question isn't "is it a good or a bad idea to have an union". It is a good idea, defenetly. It is one of the very few ways to bring democracy in our representative systems showing to the "elite" what people really want and kicking their ass if they go against that. Real questions are "what do we need ?" and "is an union the only way to obtain it ?"
As aid here, if there are other lobbys able to obtain what you want, like ISA etc, an union is not the priority. Though power concentration is never good, it can be a right thing that an union looks what ISA does, gives its opinion and reciprocally.
But if they have a limit and need to be helped to have enough strengh, an union can be a great solution.
Above all : never expect an union to answer to all your troubles. An union is only made of people. If it is dysfonctionnal don't cry seating in your chair. Stand up, join the union and change what has to be changed. If it doesn't work, make an other union. Don't wait for the hierarchy to do what needs to be done, get into the hierarchy and do it, that's the most fundamental dynamic of an union so of course it works inside an union too.
So to the question :
A good answer could be : all of you. Since the beggining make an union based on collective lead, don't wait for a pyramidal system to be good. Give short lived mandates when you need one voice to be heard on a subject to avoid a total cacophony. It's gonna be a mess, lot of votes and so, one of the side effect will be a slow efficiency but you'll be able to avoid a toxic leadership and when everybody will agree you'll have an huge strengh. That's how, in my opinion, an union has to be done
That were my two cents