Plants are not "doused" in Roundup, or more precisely, its active ingredient glyphosate. Relatively small amounts of glyphosate are applied as weeds emerge. These die and do not compete against emerging glyphosate resistant crops. Glyphosate is amazingly non-toxic to humans or any other animals. Acute effects are only seen at relatively high doses. The LD50 (the dose that kills half of the rats that consume the dose) is about 5000 mg/kg of body weight. In other words, if you weigh 200 lbs you'd have to drink about two pounds of the 41% commercial concentrate to have a 50% chance of dying. Of course, it is not recommended-- ask any of the hundreds of people that have tried to commit suicide by drinking it. It takes a good dose to cause problems. Look up "glyphosate" and "suicide" in PubMed.
The woman in the YouTube video you sent is Dr. Stephanie Seneff. She is a computer scientist in the Artificial Intelligence Laboratory at MIT. She is not a plant scientist, molecular biologist or expert in human disease. She uses the MIT affiliation and a Ph.D. to create arguments from authority without evidence. Her evidence is largely correlation. She claims that glyphosate causes autism. And obesity. And Parkinsons. And depression. And ADHD. And several other ailments.
She explains their effect being caused by "Exogenous Semiotic Entropy", a phrase if googled gives you her paper in Entropy, a low/no impact physics journal that has a reputation of publishing anything for a fee. It claims peer review, but no biologist or medical researcher reviewed the work. The phrase Exogenous Semiotic Entropy sounds fancy, but she's the first person to use it.
The big problem with glyphosate is not physiological, it is resistant weeds. Fortunately new solutions are in the works. Glyphosate is a great tool for farmers, keeping labor and fuels costs lower, plus it allows for "no-till" farming, saving valuable topsoil.