Of course, one might object that such marriages are morally wrong. In fact, insofar as entering into a marriage is an undertaking of serious commitment, those arranged “marriages” where either party does not consent are not really marriages—they are invalid for the same reason that coerced “contracts” are non-binding. But it is certainly possible for a couple to freely undertake to please their parents or to entrust the choice of a marriage partner to parents. After all, one might reasonably think that our own insight into ourselves is often less clear than the insight that others close to us have into us, and so we might reasonably allow that our parents might make a wiser choice than we, assuming they share our values and hence can be counted on to make the decision in light of considerations that we endorse. So it is certainly possible for an arranged marriage to be freely consented to.
On the permissibility of sex without romantic love, it is worth noting that even those who link sex with love, do not argue that sex without fully matured romantic love is impermissible. Romantic love finds its consummation in sexual union, but romantic love can continue to develop past its consummation. The union as one flesh may be complete, but the interpersonal union almost always needs to grow in other respects. A requirement that one marry only when romantic love is fully developed in every respect would prohibit almost every, perhaps every, marriage that has taken place.
At the same time, love is always a duty, and the love needs to be appropriate to the relationship. Thus it is one’s duty to love the person whom one is to marry, and it is a duty to love the person in the way appropriate to the person whom one is to marry. Of course, if one does not know anything about this person, the love cannot be very specifically developed. But it can involve the three aspects of all love: one has a disposition to benefit this person (should one find out what the person needs), one appreciates the other at least as a person, a creature of God, a fellow human being and someone with whom one can engage in sexual activity, and one intends that union with this person (the sexual aspects of this union may be the easiest to intend for a young and sexually curious person!) All the while, one can remain open to the mystery, the surprise of the other person. And in this way, the arranged marriage is not that different from an unarranged “love match”. In a love match, too, one must remain open to the enfolding mystery of the other person, traditionally including even a lack of sexual knowledge of the other person. And in any case, marriage and sex themselves can change people in unpredictable ways, and some of the knowledge of the person prior to marriage is likely irrelevant. Every love must involve a willingness to adjust its form to the changes in the beloved and in the relationship, and must remain open to new things.
It is not so much wrong to marry someone that one does not love as it is wrong not to love the person one marries. Love is required of us always, under all circumstances. It is wrong not to love the person one shakes hands with, the person one sentences to twenty years in jail, or the person one marries. Of course a different form of love is required in each case. However, what primarily distinguishes the different forms of love is the type of real union that the love is directed towards and the aspects under which the beloved is appreciated. If one marries, one ought to have a directedness towards sexual and personal union with the other person, and an appreciation of the other person insofar as this person can be united with. But for this one needs only to know the other person as a fellow human being of the opposite sex.