I mean, he has a fair point, from the outside anyway.
It has been shown that for most Noble's of this world, personal gain is top priority. What she gains from protecting the other is a valid question from this perspective.
And because she has behaved mostly like any other noble (for the most part) and because of her "villainous" disposition, he has every reason to believe she is no different, if not worse.
In fact, if she would actually open up to him and explain, he would be a hell of a lot more likely to be happy to help her. It's been shown that he has feelings for who she "use to be," and since her true personality is closer to that, he will be all for her actually being that now, instead of the persona she puts on as a "noblewomen".