A Weed is merely in the eye of the beholder...

"A weed is not so much a plant in the wrong place, it is a plant growing where it is not wanted" - Gardening Manual for Canada

I have to agree that I am not a vigilante weed murderer. I used to be, until I tossed 6 or 7 flourishing oriental poppy plants.
Since then I tended to be a bit more lax about what was growing in my garden.. Many herbs and useful plants are weeds by definition, but some can actually benefit the garden or gardener. I live between a field of hundreds of acres of unkept, unmaintained lands, and a county forest, which depending on the direction of the wind, I could have trilliums growing in the shadier portions of the yard, to ugly plantain plants. Some weeds are down right ugly, and others are actually pretty attractive, field poppies are gorgeous in bloom and can very easily get out of hand, but they attract hover flies and insect eating birds. Certain clovers benefit garden soil by adding nitrogen through their roots. Other local weeds provide cover for birds and other wildlife. Sunflowers are weeds, yet they attract birds and provide us with seeds, not to mention they are very beautiful in fields.