What is a weed?

What is a weed? Is weed just a mean term for a plant we don't happen to like? 

Merriam-Webster defines a weed this way:

a plant that is not valued where it is growing and is usually of vigorous growth

especially : one that tends to overgrow or choke out more desirable plants

Similarly, the Encyclopedia Britannica says: 

general term for any plant growing where it is not wanted. Ever since humans first attempted the cultivation of plants, they have had to fight the invasion by weeds into areas chosen for crops. Some unwanted plants later were found to have virtues not originally suspected and so were removed from the category of weeds and taken under cultivation. Other cultivated plants, when transplanted to new climates, escaped cultivation and became weeds or invasive species. The category of weeds thus is ever changing, and the term is a relative one.

So yeah, they're plants we don't happen to find useful, as food, ornament, construction supply, etc. Worse, they tend to "choke out more desirable plants." 

Is it insulting to call a plant a weed, then, just because we don't like it? No. Plants have no minds and no feelings and so you can call them whatever you want. 

Some people will defend weeds. They may point to particular ones that are actually useful (dandelions, for one, are edible), or are important for wildlife (especially as pollinators). That argument, however, isn't saying that weeds are good; it's saying that things we think of as weeds are actually not, because they have an important purpose. 

Other people just like weeds because they are what nature would do if we weren't interfering. In the comic strip Miss Peach, scrawny weird kid Arthur was known for growing a weed garden. The character seemed to find identification with the unwanted plants. Perhaps Arthur thought that, like a weed, he was useless and ugly, but darn it, he was also persistent! Ironically, cartoonist Mell Lazarus said Arthur was his most popular character.

But are any people really like weeds? Should we not agree with Ars Nova, who sang "Fields of People / There's no such thing as a weed"?  

Yes and no; yes, because all humans have an intrinsic value and natural rights; no, we shouldn't, because it's an inexact analogy. A decent person can turn bad and become a vile slob; a sinner can reform. But whatever stinkweed does, it's never going to be a strawberry rhubarb pie.

The main thing about weeds is that they grow like, well, weeds. It's a symbol of this fallen world that the plants that help us to survive and thrive have to be brought along with effort, while the useless ones proliferate like crazy. No one ever found a field that just automatically produced delicious potatoes or amazing rows of corn.

Sure, sometimes you can find wild blueberries or bunches of coconut trees or other wonderful things, but those are the natural exception rather than the rule. One estimate says that only around 10 million humans could survive if we were all hunter-gatherers. That's roughly the population of Michigan, for the entire planet. And fewer would survive if they were vegetarians. 

Modern agriculture (and aquaculture and animal husbandry etc.) gets the credit for the survival of the other 6,990,000 of us. 

Seeing how vital plants are for us, heck yes, there are weeds. We ought to make sure there's nothing particularly useful about them before we murder them, but then it's fair game. Bring on the corn flakes! Say no to stinkweed flakes!