[Paraphrasing:]
You can’t out-maneuver them. You can’t destroy them. If you damage them, the essence of what they are remains — they reorganize and keep coming... eventually you will weaken — your resolve will be gone... they are relentless!
.....
If you can’t take a little bloody nose — maybe you had better go back home and crawl under your bed. It’s not safe out here. It’s wondrous — with rewards to satiate desires both subtle and gross — but it is NOT for the timid.
There are ways. The first thing to recognize is the extent to which they operate off other people's money. They is their vulnerability.
In Wisconsin, a good first blow was landed by the Republicans in prohibiting mandatory dues withholding for public employee unions. Given a choice, public employees don't like the idea of sending in union dues. This cripples the union's activism.
A second thing would be to figure out how to eliminate the network of "non profit" organizations that the left uses to get their activism done. One way would be to just simply eliminate tax deductions for giving to non-profits.