When a Catholic receives the sacraments of Holy Communion and Confession they encounter Jesus Christ personally, in one instance in visible forms of bread and wine and in the other through the ministry of the priest. During such encounters, the highest reverence must be accorded to Our Lord and in earlier times this was manifested in part through the practice of kneeling at the altar and confessional grille.
Communion is nowadays often received standing and in the hand, while Confession, especially for the young, frequently involves the priest and penitent speaking to each other face to face. It could be argued, however, that to dispense with kneeling is to discard an external act that helps to dispose the faithful to such interior dispositions as humility, receptivity, reverence, fear of God and surrender. These are the dispositions to be sought when receiving the sacraments, kneeling or otherwise.
In Confession, penitents are assisted by kneeling in anonymity, and they have the canonical right to a fixed grille. Similarly, if Catholics can kneel for Communion without causing chaos, then why try to stop them?
Not all traditions are wrong and not all innovations are right, and perhaps altar rails were not such a bad idea after all.