It seems to me that there are several issues, some of which have been much commented on, others not at all.
- To what extent is it permissible to criticise the Holy Father?
- What is the meaning of the washing of the feet?
- Is it prudent for the Holy Father to disregard liturgical law?
- Should the Liturgy be used as a means to an end, other than the worship of the Triune God?
- Is it pharisaical to cavil at the Holy Father's gesture?
For what it is worth (and as ever, I rely on my well-informed and well-intentioned readers to let me know when I've got it wrong) here are my views on these topics.
1 We owe the Holy Father love and loyalty by virtue of his office and the healthy starting assumption is that he is right; however to imagine that he is impeccable is wrong, and still more wrong is to imagine that his prudential judgements are infallible. Moreover, we have a duty to make our concerns known to our spiritual superiors, and in order to do that, we have a responsibility to be clear about what they are, which may include discussing concerns with a view to gaining that clarity - always in charity of course (and that is where I have problems with some of the knee-jerk responses I have seen).
2 Is the symbolism of the Washing of the Feet specifically to do with the washing of the Apostles (and thus first bishops') feet? Or is it simply Our Lord's humility in washing the dirty feet of fallen humanity that is the point? I think, as with so much symbolism, that the meaning of the Washing of Feet on Maundy Thursday is rich and multilayered; and that this, therefore, is not an either/or question. In my view Pope Francis emphasised one aspect of its meaning very dramatically, and sent a powerful message to the world in so doing. (As it happens, I think that message would have been even more powerful had he employed other traditional symbols: a Pope in full regalia, red shoes and triple crown included, washing the feet of those youths would have been even more extraordinary!)
3 Here is where a lot of the problems lie. There is no doubt that the Holy Father is above liturgical law, in the sense that he can promulgate and rescind it. But I do not think it prudent to have a law and disregard it. It risks setting a precedent that is (I suspect) unintended. Further, given the particular context (his succeeding a Pontiff who clearly was trying to restore order and dignity to Liturgical praxis) it risks sending a sign of a change of policy, undermining the work of his predecessor. This has been much debated, so I will say no more about it here, having made my position clear.
4 This issue is something I have not seen debated. The Liturgy is for the worship of God. It is ordered to what Our Lord called the first and greatest commandment: to love the Lord our God with our whole heart, mind and soul. So my concern was that to use the Liturgy as a tool for something else - however good that something else may be, such as demonstrating humility, charity etc - would be problematic. However, re-reading parts of the Catechism, it is clear that catechesis is integral to the Liturgy (CCC §1074-5), so I think my concerns here may have been based on too restrictive an understanding of the purpose of Liturgy.
5 It is easy (and, I think, quite cheap) to liken those of us who are concerned about the Holy Father's action on this occasion to the Pharisees. But if one looks at what Our Lord criticised the Pharisees for, it seems to have been two things. One was hypocrisy: pretending to be good and holy when in fact they were not; the other is legalism: using their own man-made rules to lay burdens on others and excuse themselves. I do not think the comparison works. It is not those who have made the rules who are complaining about the Holy Father, rather those subject to them. To take the logic of the Pharasaic accusation to its conclusion, we would dispense all priests from all liturgical rules (if they felt they wished to break them for some purpose that seems good to them), and that is clearly a nonsense. Further, the motives of many of those who are concerned are a love of the Church, a love of the Liturgy, a spirit of obedience, and solidarity with those priests who have obeyed this law (and been on the receiving end of much grief) when it would have been easier not to do so. I do not think the parallel with the Pharisees stands.
So all in all, I think the Holy Father made a great and powerful gesture on Maundy Thursday, but that he was ill-advised to do it without going through the process of publicly changing or suspending the law, or taking the gesture outside of the liturgical context, within which it is governed by law.
For whilst his sign of humility, charity and forgiveness was remarkable and much-needed, he omitted to model that other great virtue: obedience. It strikes me as no coincidence that obedience figures so strongly in the scriptural explanations of Our Lord's original Maundy Thursday; and it is certainly a lesson that the current generation, within and beyond the Church, desperately needs to learn.
My hope is that someone will discretely be able to tell the Holy Father of the unintended consequences of his action: for I am sure he has the humility to learn from this, and to continue his proclamation of a vibrant Catholicism with a focus on practical charity, in ways that do not cause unintended and unwanted effects.