How does contraception affect vocations?

It might not be as simply obvious as it seems.

For instance:

Now, because of artificial contraception, the whole underlying assumptions and expectations about marriage have shifted. Marriage is no longer a way to give all, but a way to have it all. Therefore, when a young person today considers a religious vocation, they are not choosing between different paths of self-sacrifice; they are choosing between a life that seems to have it all and a life that seems to have nothing. They must choose between a home in the suburbs, 2.5 nice children, and a double income or total self denial. The choice is between a familiar form of hedonism or an inexplicable form of heroism.

Read a fascinating look at the topic by Fr. Dwight Longenecker here.