Then they should exert themselves to be sattvic and self-disciplined and imbibe a rational frame of mind as taught by Vasishta, Buddha and Swami Vivekananda. Until they do that , they should stop their preaching.
I'm sure the Parsees would be happy to hear you say their religion is dead. I don't know of any religion other than tribal beliefs and stuff like that which doesn't have some scripture. . The way I see it, some inspired person sees something, and they try to describe it - that is the origin of scriptures. They have an experience and try to explain what they've seen in words. Obviously, the manner of description will be dependent on the culture and knowledge which exists in the given time/place context. Thus most of the world's scriptures which date from a pre-scientific era can't be relied upon for accuracy in things like the origin of the universe, the structure of the physical universe etc. Nor can they neccesarily be relied on as a moral guide to life, because our ideas of what is moral and immoral are continually changing as human societies progress and our knowledge increases. Example of this is in St.Paul's advocacy of slavery. To-day that would be quite unacceptable, and I doubt anyone with an ounce of intelligence would support such a stance. It would be insane to imagine that because the bible is said to be the work of the holy spirit that every single thing in it is right, and the same is true of all scriptures from all cultures.
Excerpts from The Code of Manu, on evolution ... regarding the progression of Spirit (Life) through the various material forms: "The first germ of life was developed by water and heat" (Manu, book i., sloka 8). "Water ascends toward the sky in vapors; from the sun it descends in rain, from the rain are born the plants, and from the plants, animals" (book iii., sloka 76). "Each being acquires the qualities of the one which immediately precedes it, in such a manner that the farther a being gets away from the primal atom of its series, the more he is possessed of qualities and perfections" (book i., sloka 20). "Man will traverse the universe, gradually ascending, and passing through the rocks, the plants, the worms, insects, fish, serpents, tortoises, wild animals, cattle, and higher animals. . . . Such is the inferior degree"(Ibid.). "These are the transformations declared, from the plant up to Brahma, which have to take place in his world" (Ibid.).