I agree, that's why I asked for other people's augments against them.
And of course you are correct, unions are not perfect and sometimes are downright stupid (your two examples). Just because something is not perfect is not a reason to not have it.
It's just a good reason to improve it.
On the whole, unions (including their sometimes stupid rules) are better that not unions, and I have never seen a compelling argument otherwise (other than the two reasons I mentioned in my original post, which are not valid)
I think unions are positive or negative on a case-by-case basis. Given the value of human life, safety-critical industries almost always benefit from union presence but Hollywood for example seems to take on unions as a burgeoning cost of doing business without them providing much in the way of real value. I don't think they're universally good or bad.