Is this plant a weed and poisonous

Yes (at least in my mind) and Yes

The type that grows wild on the west coast is poisonous. I don't know about the hybrids.

They are all poisonous, every part of them, but a few species are beautiful and grown for their flowers.

Why are they sold in nurseries if they are poisonous?

Most plants are poisonous to some degree. The nurseries would be sad empty places if they only sold plants that were edible.

Daisy is correct. Many of our common houseplants are very poisonous.
http://www.guide-to-houseplant...

DaisyI said:Most plants are poisonous to some degree. The nurseries would be sad empty places if they only sold plants that were edible.

I have grown tons of potentially poisonous plants since I started gardening, I don't eat them, my kids and grandkids have never tried eating them and neither have my cats, dogs or chickens. I wear garden glows and wash my hands when I come inside.

BeKind said:Why are they sold in nurseries if they are poisonous?

Hmmm....
Would you insist that all nurseries only carry vegetables?

While an edible landscape is a desirable thing, growing flowers for the pollinators helps ensure a better crop from the kitchen garden.

Datura would be one of the plants grown in the pharmacopeia garden, alongside other toxic plants like foxglove...

And then.... There's the highly poisonous plants with no apparent use, like oleander, castor bean, and aconitium.

And even these.... Have some use....
I used to add some castor beans to the melon seeds to prevent rodents....

And.... People living in high concentrations of deer.... Really can't grow much else...
http://www.stonethegardener.co...

Most landscape plants are toxic, or at least undigestible &/or unpalatable. Otherwise, they would be dinner.

Datura is a genus name, within with are many different species. One would need to discuss each species in regard to the location in which it is growing to determine if it is a native plant in native location, or otherwise.

D. metel is a highly prized, cultivated species with many named cultivars:
https://garden.org/plants/sear...

Technically, aren't tomatoes a member of the nightshade family? Or is it some other edible plant that belongs?

stone said:

And then.... There's the highly poisonous plants with no apparent use, like oleander, castor bean, and aconitium.

Oleander (heart glycosides), castor bean (constipation), and aconitum (pain killer) all have medicinal qualities, but are so extremely toxic it is not recommended that one muck around with them.

Best way to grow potentially dangerous plants is to educate yourself about their toxicity. Some are quite bitter and unpalatable (a natural deterrent) while others can be more easily accidentally ingested. I have quite a few toxic plants in my herb garden (as well as the common flowers noted above) and give them the respect they deserve.