Perhaps I'm splitting semantic hairs, but what is "regular" fiction? Science fiction is a subset of fiction, but it is fiction nonetheless. If a novel is set in 18th Century Europe is it then not "regular" fiction? Is it "only" historical fiction? Only "European" fiction?
"Science fiction books" are a subset of "fiction books".
"Fiction" is a radically constrained subset of "science fiction".
One of the reasons I enjoy science fiction so much is that in the hands of a master, it has much more possibility to be truly powerful and good literature than the genres that limit themselves. Like any other ingredient, it can either make the dish or ruin it, but the ingredient should not be judged by the ruined dishes people make with it.
(Example: I recommend A Deepness in the Sky for an interesting literary treatment on slavery that goes well beyond "Slavery is bad, mm'kay?" and with relevance well beyond the usual historical issues. Try it in non-sci-fi and it would either fail or be silly.)
The Martian Chronicles is SF, maybe not Hard SF, but SF.
That's where the limit between SF and fantastic is blury, but in that regard Dick is sometimes more fantasy, or not so science (consider Time Out of Joint for instance, probable inspiration for the Truman Show).
This isn't correct. Science fiction routinely has elements that violate the laws of physics and nature as we know them today. Having actual science is in most cases a disqualifier (there is some SF that sticks to science, but that's hardly the norm). If your imagination is required for the work to make sense, it's probably not science.
If I had a dime for every science fiction story with super-realistic spaceflight yet also with completely unexplained "ansible" technology that allows instantaneous communication with anyone in the universe....