What is ironic about Capulets praise of Friar Laurence in act 4 scene 2?

Capulet praises Friar Laurence for marrying Juliet to Romeo, unaware that this very act is the root cause of the tragic events that befall both families. The irony lies in the fact that Capulet believes Friar Laurence has brought happiness and joy to the families, while in reality, his actions have unknowingly set the stage for their downfall.