disciplinary infallibility

I have just added a link to a great blog on the side, the Lidless Eye Inquisition, which describes itself as

A weblog dedicated to the exposure of the crackpots of the lunatic self-styled 'traditionalist' fringe who disingenuously pose as faithful Catholics.

and has on its latest post

"If she [the Church] were able to prescribe or command or tolerate in her discipline something against faith and morals, or something which tended to the detriment of the Church or to the harm of the faithful, she would turn away from her divine mission, which would be impossible.

Ah, hmm. So from the Catholic Encyclopedia entry

The authors of these treatises decide unanimously in favour of a negative and indirect rather than a positive and direct infallibility, inasmuch as in her general discipline, i. e. the common laws imposed on all the faithful, the Church can prescribe nothing that would be contrary to the natural or the Divine law, nor prohibit anything that the natural or the Divine law would exact. If well understood this thesis is undeniable; it amounts to saying that the Church does not and cannot impose practical directions contradictory of her own teaching.

In its own laws, the Church cannot impose anything that is contrary to what it is supposed to teach. However, it does not mean that everything it imposes must be perfect or the best. What is perfection anyway? And so ...

From the disciplinary infallibility of the Church, correctly undersood as an indirect consequence of her doctrinal infallibility, it follows that she cannot be rightly accused of introducing into her discipline anything opposed to the Divine law; the most remarkable instance of this being the suppression of the chalice in the Communion of the laity. This has often been violently attacked as contrary to the Gospel. Concerning it the Council of Constance (1415) declared (Sess. XIII): "The claim that it is sacrilegious or illicit to observe this custom or law [Communion under one kind] must be regarded as erroneous, and those who obstinately affirm it must be cast aside as heretics."

Take for example communion on the hand. In this day, I see lots of people coming up to receive communion in a very sloppy manner, and I firmly support a tightening of discipline to encourage tongue+kneeling reception for its value in teaching the laity the proper dispositions. However, I cannot, for the life of me, see how communion on hand is a sacrilege and hence innately sinful, innately harmful and innately detrimental to the Church.