That's why I will often have an OTP that doesn't actually have any of my favorite characters either. Temari/Shikamaru has been my Naruto OTP pretty much ever since I saw this page, but it's only fairly recently, in the past month or so, that Temari has managed to claw her way into my brain as one of my favorite characters. I fell in love with the character of their relationship before I did either of the characters themselves. (Although, of course, I was always aware that they were awesome.)
On the other hand, both Sasuke and SasuSaku needed time for me to warm to them (and Sakura herself took even longer). For a long time, I didn't really understand the depth of the relationship. On the other hand, I've always enjoyed the relationship between Sasuke and Kakashi, although I only actually slash them as an exercise in crack.
Which brings me to the topic of non-canon pairings. I tend to think of them as the equivalent of placing characters in an AU setting. You've changed something about their emotional environment--the sexuality of a character, perhaps, or the amount of romance in their relationship with someone. You are still under an obligation to write the characters as true to themselves as possible within this changed framework.
Some people enjoy the AU relationship more than the canon one. I don't have a problem with this, so long as they keep two things in mind. One: their OTP isn't canon. Two: they still have to write the characters as true to canon as possible. When either your AU or the canon must bend--it needs to be your AU. Do not stick Hinata with Neji and Sakura with Lee and claim that this makes NaruSasu canon. It doesn't. It makes you an annoying fanthing. Sideshipping is bad, okay?
But of course, from this you get all sorts of absurd pairing wars. I don't mind NaruSasu. I even like it sometimes, but while I generally prefer the canon version of them, their relationship is a powerful enough one that the popular romantic AU version can be very interesting when done well. Unfortunately, there are many fancrazies who are convinced that it is canon, and in order to support this, they bend the actual canon every which way--usually damaging the characters involved as they do so.
LeeSaku in particular bothers me because it almost invariably bends the canon rather than the AU. Sakura is not going to decide that she never loved Sasuke after all/Lee is a better man than him anyway so she should just give up/whatever. Lee is not magically in love with Sakura despite barely knowing her; he is using her as a goal. But the majority of LeeSaku fanfic has Sakura deciding that she never loved Sasuke after all/Sasuke is a horrible person and because of this she'll automagically stop loving him, and Lee, for his part, has always been totally and completely in love with Sakura and will make a perfect boyfriend unlike that Sasuke, who is either a) a horrible bastard who could never love another human being or b) clearly totally gay for Naruto and thus doesn't care about Sakura at all.
I do not mind the AU LeeSaku in and of itself, just the fact that it so often bends the canon.
The matter is thornier in Bleach fandom. As far as I'm concerned, IchiRuki is Bleach fandom's equivalent of NaruSasu. Canonically, it does not exist as a romance. But it's a complex, fascinating, and powerful relationship, and I personally enjoy the romantic AU version of it very much. However, like NaruSasu, it has to be handled with caution lest it turn into pointless sap that destroys both characters as well as the essential character of the relationship. But there's another issue: because it's het (and it pairs the hero with the woman who seems to be the female lead at first), there are even more people convinced that it's canon. And things get Messy. But at least the pairing wars don't get as vicious as the ones in Naruto.
And then there's Harry Potter fandom, which makes FMA fandom look sane. Fancrazies, it is up to you to adjust your AUs to match the author's canon, not the other way around. Grow the hell up.
In conclusion: fans of non-canon pairings are not intrinsically evil or stupid, but the burden of keeping the canon intact is on them.