Confirmation bias surely depends on the data set, ie sample size, initial feelings, final result?
I'm not quite sure what this question is getting at. This is the definition of confirmation bias from the Wiki entry, which seems to be pretty good.
Confirmation bias, also called confirmatory bias or myside bias, is the tendency to search for, interpret, favor, and recall information in a way that confirms one's preexisting beliefs or hypotheses. It is a type of cognitive bias and a systematic error of inductive reasoning. People display this bias when they gather or remember information selectively, or when they interpret it in a biased way. The effect is stronger for emotionally charged issues and for deeply entrenched beliefs.
A large sample size won't help correct any confirmation bias - if the sample isn't done in a statistically sound way it will be part of the bias. It will just be a skewed set (and those can contain millions of data points).
Essentially I don't think you'll ever settle this argument. There will be people who want to believe in LAFS and so they'll believe it. If they're told that other people have experienced the lightning bolt and it turned out not to be lasting love, they'll just say "oh well you didn't really feel it, did you.". Because the whole thing is subjective, you won't settle it one way or the other.