Actually, not all instances portray Lord Capulet as being an overruling father. Capulet shows us that he takes Juliet's interests and wishes to heart. We especially see this in the first scene in which we see him talking to Paris. When Paris asks for his daughter's hand in marriage for the second time, Capulet says that he still thinks she is too young and would prefer to see her wait until she is sixteen to marry, as we see in his lines:
She hath not seen the change of fourteen years;
Let two more summers wither in their pride
Ere we think her ripe to be a bride. (I.iii.9-11)
Not only that, he says that his consent is only a small factor in the bargain and Juliet's own consent is what is most important, as we see in his lines, "But woo her, gentle Paris, get her heart; /
My will to her consent is but a part" (16-17). Hence, through these lines we see that Capulet, unlike an overruling father, does not wish to make any decision concerning his daughter's life that Juliet, herself, will not also be pleased with.
Capulet changes his mind about seeing Juliet married so early because he sees her as grieving severely over Tybalt's death. In fact, he thinks that the extent of her grief is putting her in danger, as Paris explains to Friar Laurence:
Immoderately she weeps for Tybalt's death,
Now, sir, her father counts it dangerous
That she do give her sorrow so much sway,
And in his wisdom hastes our marriage. (IV.i.6-11)
Hence, in wedding her to Paris, Capulet is trying to do what he thinks best for his daughter by distracting her from her grief.
However, characteristic of all fathers of this time period, he is very shocked when she refuses to do his bidding. Here is where he goes a bit overboard. A more rational father might have rethought his decision and tried to think of another solution to help Juliet out of her grief. A more rational father might have realized that marrying her against her will might have increased her grief rather than lessened it. Hence, when Capulet threatens to throw Juliet out for refusing to marry Paris, saying, "Out, you green-sickness carrion! Out, you baggage!," he does act as an overruling father.