Because if this at most partially correct, why aren’t aren’t doctors suggesting the same for us? since majority of the parasites that normally infect our dogs do infect people, with all the same negative health effects.
These are medical questions that you should ask your vet and your family doctor. In the meantime, we know that both humans and dogs and wild animals can and do get infected with rabies. We also know that in order to protect humans from this horrible disease we have laws to vaccinate dogs. Having dogs—the direct link between the wild and humans—vaccinated seems to be an adequate buffer to protect humans.
Using rabies as an example, my guess is this extends to other problems as well. Also, going by the things I’ve experienced with my dog, there is more than one kind of parasite one should protect one’s dog against. There is heartworm, a problem my vet tells me is very difficult to treat once the dog has it but easy to protect against. And there are nits or whatever those bugs are called that live on the skin of dogs—again easy to treat in dogs.
You mention “deworming.” I’m not sure if you mean intestinal worms, perhaps. Treat the dog and the human community is pretty much protected, depending (obviously) on the hygiene of your person and residence. As stated above, these are questions that can be best answered by your vet and family physician. Not only do they have the medical training, they also have a face-to-face relationship with you and public accountability to a degree no stranger on the internet will ever have.