It's not a theory -.-
Not arguing with you about it - it is
possible to legit FC - but if you are hit from offscreen with CS, from the bridge for example, there is no assumption of 'legit' that comes to mind. I know for a fact they have to have seen you to begin with...
I'm not denying the fact that there are duelers that are patient enough to have perfected (as much as you can) the technique - same with many skills - but I'd say at least 99% of pubs perform the technique with 'help'. Maybe I'm too harsh with my figure, but it could very well be generous.
Those 'strategies' people use are usually in response to offscreen CS (sorb, res auras, Doom, Lo's, etc) at least from what I read and have seen. I'd like to think alot of people (posters who said something about FC in this thread and others) don't go around BM'ing Java's in anticipation of 'hax'. Maybe that's what you are referring to with assumptions, regardless most of 'em do it...
I go with the general thinking:
Innocent until proven guilty (or until I'm hit from the bridge)
Reactive, I guess.