Poor Friar Laurence! He's doing the best he can in the situation to give good advice to the two lovers. The problem is that he doesn't have influence in either household. The kids are running to him at the church, but he doesn't make an attempt to step in between the two families to become a mediator. Instead, he exacerbates the situation by teaching the kids to solve problems in secret. The secret marriage causes more stress and heart-ache for Juliet because her father wants her to marry another man; Romeo confuses his friends by not telling them (most importantly Mercutio) about his marriage; and because of the lack of information that other characters have, they make fatal decisions. For example, if Mercutio had known about the marriage, he may have understood Romeo's behavior towards Tybalt in the fight scene where he dies. And, had someone else other than the nurse known about the marriage, maybe they wouldn't have felt like the had to fake Juliet's death (which was just another secret stemming from the first).
So, since Friar Laurence concocted all of these secets, he can be traced back as the author of the consequences.
Escellent question. I should use it in my classes.