Mrs Birling makes her opinions of the working class clear: that they will lie, they will accept stolen money and they are to Blame for their one situation. If Mrs Birling has such a low opinion of the people she is meant to be helping, why is she involved in the charity? We can infer that her ulterior motive to work on the committee has more to do with how it looks to chair such a committee and wield power, rather than be driven by the desire to help other people.