Due to those spines, and the fact most people don't keep gas welding gloves around the house, I don't recommend pulling them out anyway if you're faced with a clump up to your thighs of this size or bigger:
For some reason, I had it in my mind to just yank them out (like I do most weeds). It's only the *challenge of the gloves* that got me, since I pride myself on finding the best garden-use gloves for the lowest price I can locally (my hands are big so not all gloves fit).
I ended up soaking them with the garden hose, shoving the nozzle right at the root, and going down, oh, about six inches, which allowed them to be pulled out easily *with* very (very) thick (and long) gloves.
If you didn't have long and thick gloves (absolutely nothing in the box stores would protect you); you'd resort to more mechanical means.
Even with excellent gloves and a good soaking, I had to dig at one bull thistle clump with hand equipment, to get it out:
Based on my reading of the habits of bull thistle, it seems that they only live two years, and that their seeds don't generally travel all that far (only a few feet as they're very delicate).
So, had I headed the flowers, then I'd only have to worry about these yearlings (which only form low-lying rosettes):