beggar's opera act 1

The first act of Beggar's opera left me feeling confused about the play. I think it starts off in an awkward place because the writer wants the reader to draw his or her own conclusions about all the characters ,who ,at this point are undeveloped. I kinda felt like I was coming in on the middle of the play. I had some questions like, why are her parents calling Polly a slut and a hussy all the time? Compared to today's standard she hadn't acted like a slut at all. why were her parents mad at her for getting married? What was wrong with the guy she'd picked? The first act left me feeling bad for Polly, hating her parents, and thinking that Macheath was a good guy.