The evidence is simply overwhelming. Consider the following:
Fact #1: The vaccines do not stop the spread of Covid infection.
There are countless breakthrough cases being reported all over the world. Moreover, some of the most vaccinated countries have the highest rates of infection transmission. Israel is a case in point. An early leader in vaccination, it also has the highest infection rate on the planet. And this by a large margin. Needless to say, most of the infected have been vaccinated.
A recent piece in the National Geographic describes just how serious the situation is. The title of the article is "Evidence mounts that people with breakthrough infections can spread Delta easily." The subtitle says it all: "A new study finds that this dominant variant can grow in the noses of vaccinated people as strongly as in unvaccinated people."
In other words, as far as the transmissibility of the Delta variant is concerned vaccination makes no difference.