I have been a Union member for almost all my working life, and thanks to their support, I kept my job when unreasonable behaviour from a couple of managers would have meant me losing it unfairly.
Of course there are extremists, but there are in every walk of life, that's simply a fact.
But you can't tar everyone with the same brush, that is unreasonable.
The essential requirement of Unions in the modern workplace is to ensure that workers are treated properly and kept safe - that has never changed.