During my working career I had quite a few experiences with unionism.
I had a few issues ....
I never liked the fact that union halls were not owned by the members themselves. When Mine Mill Union was ousted by the Steelworkers union in Sudbury in the 1960's, the local union membership did not inherit the Mine Mill union halls, and the same workforce but with different union representation (Steelworkers) had to finance and build new union halls.
I never liked the idea that 5 cents of every dollar in dues went to the NDP political party. Although I always voted NDP, I always felt bad for those members who were voting for other parties but were actually financing another political party.
I never liked the idea that paid production bonuses were subject to union dues. I think that union dues should only be paid on the salary being earned.
I really liked the role that unions played towards ensuring a safe workplace.
As a local union president, I always noticed that members constantly complained about the union but never showed up at regular scheduled union meetings. The only time union members took an interest in what was happening at the union hall was during contract negotiations.
The largest mistake that unions made was to not have purchased a major newspaper chain. They did invest in community events such as summer camps and stuff, but they needed a loud voice within the community as well, but failed miserably.