Anyone who looks on the loss of salvation for others as the condition, as it were, on which he serves Christ will in the end only be able to turn away grumbling, because that kind of reward is contrary to the loving-kindness of God.
Fr. Ratzinger had in mind the grumblers who resent sharing salvation with non-Catholics. But what about the sluggards who are delighted by the thought, because of all that evangelization work it saves them?