I am a convinced admirer of Opus Dei, both as a practising Catholic and as a man firmly of the Left.
Corporal mortification, to get that out of the way, is an integral part of Catholic spirituality. Catholics need to re-learn moderate self-denial on Fridays, on the Wednesdays in Lent, during Holy Week, on the eves of the Church’s greatest Solemnities, and before receiving Communion, as well as the considerable exigencies on Ash Wednesday and Good Friday.
These are of a piece with the cilice (a spiked chain worn around the upper thigh) and the discipline (a small whip used on the back). Convents manufacturing such items still do a roaring trade, and the rise of Opus Dei is itself a sign that the decadent period of disdain for asceticism even within the Catholic Church is an aberration now mercifully coming to an end.
In any case, people who suggest that Ruth Kelly wears the cilice to work merely demonstrate their own ignorance. Both the cilice and the discipline are used by numeraries, who are celibate, live in Opus Dei centres, and give most of their salaries directly to Opus Dei. Kelly is clearly a supernumerary, as are seventy per cent of Opus Dei members, and so presumably mortifies the flesh in ways more acceptable to clever-clever opinion, though none the worse for that.
Opus Dei believes in the sanctification of the world, thus first anticipating and then implementing the Second Vatican Council. By contrast, its opponents believe in the secularisation of the Church, falsely presenting that as "the Spirit of Vatican II". Therefore, they oppose corporal mortification as they oppose other Opus Dei practices: beginning the day by offering it to God, daily Communion, the Rosary, the Angelus, daily examination of conscience, invocation of the Angels and the Saints, ejaculatory prayer, use of holy water, and so forth.
This is because they disagree profoundly with Opus Dei about sanctification of and through ordinary work, not least because they so look down on the people who do a great deal of ordinary work.
They disagree with Opus Dei about living a contemplative life in the middle of the world, taking everything one does with liturgical seriousness, and recognising (as any orthodox Catholic must) that every experience of the true, the good and the beautiful is in fact a religious experience. Instead, they would rather that even the Liturgy were treated with no more (or even rather less) seriousness than most people attach to a pop concert or a football match, and that even the most obviously ecstatic mystical experiences were somehow explained away by pseudo-scientific, avowedly anti-Christian means.
They disagree with Opus Dei’s (i.e., with the Catholic Church’s) definition of Christian freedom in the Aristotelian (yet profoundly Biblical) terms given definitive Catholic and commonsensical articulation by Saint Thomas Aquinas, according to which the only true freedom is in accordance with the Will of God. Instead, they would define it in secular and Modern terms, as the freedom of the individual to do as he will (provided that he agrees with them), and that as the end in itself.
They disagree with Opus Dei’s (again, simply the Church’s) doctrine of divine filiation, of recognising oneself and every other human being as a Child of God. Adopted by God’s grace and thus in some sense ipse Christus, "Christ Himself", everything we do is therefore in some sense part of the world’s redemption: the mundane is transcendent. Instead, they would rather make the transcendent mundane.
They disagree with divine filiation’s very high understanding of the dignity of each and every human life, and with its strong imperative towards evangelisation. And they disagree with its inherent imperative, both to take up the Cross, and to experience a profound joy quite unlike any momentary chemical or sexual "high" of their own formative years. Instead, they would rather "modernise" on abortion, euthanasia and stem-cell "research". They would rather trim Christianity and Catholicism to suit every other system of belief, though even then not with a view to converting anyone. And they would rather have instant gratification, on the cheap in every sense.
Sanctification through work, the living of a contemplative life in the middle of the world, Christian freedom correctly defined, and the recognition of divine filiation: these are the principles calling all Catholics to rediscover and renew, ever-more-deeply, our beginning the day by offering it to God, our frequent Communion, our daily examination of conscience, our ejaculatory prayer, our use of holy water, and our devotion to the Mother of God, to the Angels and to the Saints. And, yes, our practice of corporal mortification.
All of this is whether or not we experience any vocation to join Opus Dei, undoubtedly God’s instrument in renewing the Church in this way, but even more clearly so if this renewal becomes the norm among Catholics generally, including our witness to ecumenical partners.
So much for admiring Opus Dei as a Catholic. But how can a man of the Left possibly do so? Well, Ruth Kelly is the most prominent Opus Dei politician in the world today. The President of the Socialist International, António Guterres, has a long history in Opus Dei. Its ranks also include Squire Lance, Antonio Fontán, Paola Binetti, Llúis Foix, Mario Maiolo and Xavi Casajuana (if we count Catalan nationalism as part of the Left; it is certainly a very long way from Franco), among others.
Most of the Chilean "Chicago Boys" were not members of Opus Dei. Pinochet himself never had any affiliation with it. Of six right-wing Opus Dei politicians listed on Wikipedia, four are dead (one since 1966), whereas the three broad left-wingers listed (including two women) are all still alive. So, insofar as it has a political orientation, Opus Dei’s would seem to be towards the Left, if anything.
Much like the Catholic Church Herself, in fact. Which is yet another reason to hope, work and pray for the Catholic Church at large to become much more like Opus Dei.