The same way you reject the general concept of all the fairy, Santa Claus, Big Foot, elf, and mermaid conceptions out there even though you've never heard of all the various conceptions. I really don't see why gods are unique or should be considered an exception.
That's partially the point I was trying to make. I don't think that I have to learn about all the different fairy, Santa Claus, Bigfoot, and mermaid conceptions in the world to say that I don't believe in them; I don't have to "reject" every one of them on an individual basis simply because it happens to be believed by some people.
If I thought that idea 'X' doesn't have enough evidence to warrant belief in it and I heard that there were many other similar ideas, e.g., 'Y', 'Z', 'M', etc., that are also held to be true by some people, then I don't see why I'd have to examine every one of them before I can reach the conclusion that I don't really believe any of them to be true.
In other words, if a set of ideas contains similar elements and all of those elements make a similar assumption (in this case, the existence of an entity without sufficient evidence), I don't think it'd be unreasonable to view that one element of the set as generally representative of the others without necessarily examining all of them in detail.