Ok, ultimately the entire debate comes down to the question of 
how important the source material is in fanfiction.
	Fan fiction is in many ways a shortcut.  Rather than creating a 
whole world and set of characters to work a story, you take characters 
someone else created and work with them.  Now in some ways this is an 
advantage, since it means you can simply say Ranma and not worry about 
having to describe what he looks like and how he acts, those of us 
who've read the Manga or seen the Anime already know.  The thing is 
that this knowlege also means that we have have seen him act and react 
to various situations and drawn conclusions about him from them.  This 
does not mean that our conclusions will always be the right one's, but 
they will be the result of observation of a common source.
	I don't want to start a debate, so feel free to skip this 
example.  {I recall seeing some debate about Ukyo acting dramatically 
differently in later episodes as opposed to the one's where she was 
introduced, when her actions were as consistent as the rest of the 
characters if you made a different set of assumptions about her 
motives}
	Ultimately everything is personal.  If the writer holds to a 
different set of assumptions or feels that the story excuses the 
changes, that's their perogative.  The reader simply has to assume 
weather or not the differences present too much of a barrier for them 
to immerse their immagination in the story.  The greater the gratuitous 
deviation from the source, the more difficult it will be for the 
readers to get into the story.  And the ultimate question of weather a 
story is good or bad is weather or not the reader will be able to get 
into it.