I think of science fiction and fantasy as being a "meta-genre", they do blur together. Most science fiction conventions are really science fiction and fantasy conventions, they coexist quite well. As far as horror goes, some fits into the SF&F meta-genre, some doesn't. A horror convention includes quite a lot that you probably wouldn't find at a science fiction convention. I don't read paranormal, but I don't see why it wouldn't fit into SF&F. Angst and whining might make it annoying, but they don't seem to change the category.
Then of course there are people going tooth and claw insisting that this or that isn't "real" science fiction. The best definition of "hard science fiction" that I have seen is "science fiction that you like".
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