In general I think unions are like governments - they need to be regularly overthrown and rebuilt to ensure that they always represent the best interests of their members.
That being said, there are some obvious counter-arguments to your experiences, however they tend towards "guilds" as mentioned in another comment more than unions as I understand them.
> Oh, you want to move that folding table and a few chairs to the conference room so you can have a design meeting with the whole team? Sorry furniture movement is union-only work.
Bob grabs the table and lifts with his back, in a twisting, jerking movement. Bob is then unable to come in to work due to back pain for the next two weeks. The union keeps Bob from hurting himself unintentionally.
> Need that extra monitor moved between two adjacent cubes? Sorry, equipment relocation is union work.
Someone notices that a bunch of monitors have gone missing. Have you been burgled?! Noone has any record of where these monitors have gone, however you eventually track then down to Alice's cube where she has finally completed her dream 9-monitor nest. Phew, false alarm!
> Need to plug that new PC into the socket? Sorry, equipment installation is a union job
It gets cold in the winter, so Dan brings their own heater to put under their desk[1]. One day they forget to turn it off when going home and burns down the department;
On the other side new employees don't just materialise out of the ether. The organisation should have plenty of time to set up their working environment
[1] Funnily enough, if Dan was part of a union they would have enough bargaining power to make sure their employers provide adequate working conditions, however their manager simply filed away their request away under 'C', for "Complainers - Fire these people first"
I'm totally on your side about these examples being ridiculous, but I do like to steelman the other-sides arguments