> - Unions add more politics to an already increasingly political environment. I don't want to spend an hour or more every month in a meeting to vote on stuff I usually don't care about.
Would you prefer these decisions to be made unilaterally, without any input from you? Because that's the status quo. If you are happy with these decisions being made unilaterally, don't vote. If you aren't, you have more of a lever than you do without a union.
> - Unions cost money, and while 200$/2 weeks (which is what one big union in my country charges) might seem reasonable to you, I don't like being forced to do anything.
I'm assuming most of that money is going into a strike fund. Having a strike budget makes your negotiating position much stronger, just like how if you don't live paycheck to paycheck, your negotiating position is much stronger.
If most of that money goes into administrative expenses, you may want to consider voting to reduce those expenses.
> Unions make it harder to fire under performing employees.
Unions require management to follow a process to fire employees, under-performing or otherwise. My wife worked in a union for 8 years, and plenty of poorly performing employees were fired during that time. The difference is that they weren't fired arbitrarily. You'd appreciate protection from that, if you were to ever be fired for political, personal, retaliatory, or just purely fabricated reasons.
If your management can't figure out how to document how an employee is underperforming, and to give them notice to shape up, I'm not sure your management can be trusted with anything.
> - Unions usually end up with rules regarding who gets promoted and who doesn't. Broke your back working OT to help out the company? Well tough luck Martha came in one month before you and has priority on promotions.
Did the union make those rules, or did management make those rules in an effort to control costs, and then blame it on the union?
Unions are democratic, by the way. If you don't like tenure-based promotion, vote to change it. You have no such recourse with a manager who arbitrarily promotes people they like.