We've already had a couple of questions asking if something can be considered science fiction, and questions of this kind seem very unlikely to produce interesting or informative answers. I think they should be explicitly considered to be off-topic
I can't see how questions like that can have answers that are anything other than subjective opinions.
There isn't one generally agreed-upon definition of the term "science fiction," which makes "Is this SF?" questions functionally equivalent to asking "Which is a better dessert: chocolate or ice cream?"
There are already debates in progress here on whether topics as well-known as Star Wars, The Matrix, and Transformers are/are not SF. I highly doubt this community will ever come to one unanimous interpretation of the phrase—which makes all the "Is this SF?" questions purely subjective and completely unanswerable.
This is a Q&A site about SF, and it is perfectly reasonable to expect questions which define what SF is and what it isn't.
Of course, it would be much better to create a FAQ stating what are the criteria that must be met so that we would consider something a work of science fiction. That way we can kill all the flies at once.
OK, suppose, just for the sake of example, I ask if Bill & Ted excellent adventure can be considered as science-fiction.
Will someone will learn something from this question ? Obviously, me and maybe you (this movie is full of time travels and somewhat copes with temporal paradox, although just for the fun of it ... like the whole movie, in fact).
Will we both talk about science-fiction ? Yes, of course, to justify the fact that, like To say nothing of the dog, by Connie Willis, this movie does not uses the time travel to talk about its physical complexity (contrary to, say, Timescape), but rather as a comedy element, however using it far beyond "simple" "I get back to tomorrow to avoid my today-self to loose his keys", or at least that's what I think.
To build upon this example, science-fiction has very fuzzy borders, and this site, like any other communcation medium about science-fiction, will have to cope with these borders, are they visible (like frontier between science-fiction and fantasy) or not.
As a consequence, yes, to my mind, questions asking if X is science-fiction will always be considered as full parts of this site.