Thistles, the good, the bad and the native

When we see a plant and it is prickly, we automatically assume it is a thistle and therefore it is a bad plant. The Oxford Dictionary defines a thistle as "a widely distributed herbaceous plant of the daisy family, which typically has a prickly stem and leaves and rounded heads of purple flowers." There are 20 thistles native to Colorado and they are desirable plants? Thistles are in the Asteracea...