Why does Friar Laurence consent to Romeo's request?
Friar Laurence is essential to the plot, and it is convenient that he is able to perform marriages without the need for licenses, witnesses, blood tests, or any other modern formalities. His consent to marry Romeo to Juliet is a high hurdle that requires a suspension of disbelief on the part of Shakespeare's audience. The friar is being asked to marry Romeo in secret to a thirteen-year-old girl who belongs to the house of the Romeo's family's hated enemy the Capulets. Later this audacious friar will give Juliet a potion which will make her appear to be dead and cause her to be placed in an open tomb. His well-meaning but irresponsible interference will result in the deaths of Romeo, Juliet, and Paris.
In Act 2, Scene 3, Friar Laurence is easily persuaded to perform the marriage Romeo requests. The friar rationalizes that the marriage could be the catalyst that would bring about a reconciliation between the houses of Montague and Capulet after many centuries of hatred and conflict. He tells Romeo:
But come, young waverer, come go with me.
In one respect I'll thy assistant be,
For this alliance may so happy prove
To turn your households' rancor to pure love.