I think one of the issues here is that there are some guys around who feel a sense of entitlement on the basis of having asked you out, and if it's a (total) stranger it's difficult to tell the difference. In fact, if a total stranger approaches to ask me for a date, I tend to think they are more likely than the average population to be creepy or unpleasant.
Of the four total strangers who have approached me to ask me out in the last year or so, only one took the initial brush off ("I've got a boyfriend" - a lie, but that was the most recent and I had learned by this point) and went away. Two of them harrassed me
after I had said no for a good ten minutes or so with "why not?", asking for my phone number and so on. The remaining one trapped me on a bus, intimidated me into giving him my number, and went on to sexually assault me.
So my experience is that the truth is completely useless with a complete stranger. If a friend or acquaintance was asking me out, I might well act differently.