Of course I want to treat you with respect! But offensiveness is a tricky thing, what offends one may not offend the other. Perhaps if I read the whole story and saw it in context it would be more offensive, but the speaker is already justifying Slytherin and the Pureblood blather and other things that are presented in the HP books as unjustifiable, so that's how I took it.
Re: The beliefs and actions of (a) character(s) are not automatically those of the author.