I think the Capulets are presented as villains. They won't let their daughter do what makes her happy, causing them to be antagonists to the protagonist, Juliet. In Act 3, Scene 5, lines 155-157, Capulet says "or I will drag thee on a hurdle thither. Out, you green-sickeness carrion! out, you baggage! You tallow-face!". This means he will force her to marry Paris by dragging her in a cart meant for criminals (hurdle). He calls her a piece of dead flesh (green-sickness carrion), and a coward (tallow-face). He is so mean to her, as the average villain would be, and really for no reason at all. All Juliet did was love Romeo. She didn't kill someone or rob a bank. She loved someone. Her father practically bullied her for loving someone.