That’s a real problem. I’ve spoken to the pope himself about this, and he said he believes that 50 percent of marriages are not valid. Marriage is a sacrament. A sacrament presupposes faith. And if the couple only want a bourgeois ceremony in a church because it’s more beautiful, more romantic, than a civil ceremony, you have to ask whether there was faith, and whether they really accepted all the conditions of a valid sacramental marriage—that is, unity, exclusivity, and also indissolubility. The couples, when they get married, they want it because it’s stable. But many think, “Well, if we fail, we have the right.” And then already the principle is denied. Many canon lawyers tell me that today in our pluralistic situation we cannot presuppose that couples really assent to what the church requires. Often it is also ignorance. Therefore you have to emphasize and to strengthen prematrimonial catechesis. It’s often done in a very bureaucratic way. No, we have to provide catechesis. I know some parishes in Rome where couples have to attend catechesis, and the pastor himself does it. We must do much more in prematrimonial catechesis and use pastoral work and so on because we cannot presuppose that everybody who is a formal Christian also has the faith. It wouldn’t be realistic.
Cardinal Kasper has a longstanding habit of saying things very confidently on grounds that are not obviously adequate for the confidence, but I think it needs to be pointed out that if the Cardinal is right, doing "much more in prematrimonial catechesis" and using "pastoral work" is simply not going to cut it. The level of failure he is suggesting is so extreme that it could not possibly have come about without extraordinary and culpable negligence on the part of bishops and priests. Bishops and priests exist for the purpose of maintaining and protecting the sacramental order; what Cardinal Kasper is claiming is that they have failed on such a scale that it amounts to an outright betrayal of the laity and could reasonably be said to cry out for serious public penance on the part of bishops and priests who are guilty of letting the situation deteriorate to such an astounding degree.
In any case, as Ed Peters has noted, it is an extraordinarily irresponsible thing to toss out in a public interview as if it were a serious assessment: sacramental validity is not a trivial matter, and if you are going to make a statement like this in public, as opposed to just a private conversation, you had better be doing so on the basis of rigorously established principles and you had better be offering a considerable sight more than vague suggestions about catechesis as your solution.