It's not that I have a PROBLEM with breaking up canon couples. Heck, I DETEST most canon couples in stories where romance isn't the actual focus. It's just that in a lot of fanfics where somebody are paired up with somebody else than who they were with canonically, it's usually just written off with "they broke up". And that can be okay, but if the romance in question actually had something to say for the story, there needs to be SOME explanation. And unfortunately, that is something a lot of stories are lacking - and it looks sloppy at best.
So, I'm all for breaking up canon couples. It just gets on my nerves when people can't do it decently.