Argumentum pro: Laity can preside at certain liturgies
For example, the General Introduction to the Book of Blessings states "Blessings are part of the liturgy of the Church." (n.16). Now the Book of Blessings is replete with rites that may be conducted by lay ministers without the assistance of the ordained. Are these various rites of blessing "liturgical acts" when they are performed by the ordained, but not "liturgical acts" when they are performed by laity? The Catechism of the Catholic Church states "lay people may preside at certain blessings." CCC 1669, emphasis added.
The Catechism also states "The whole liturgical life of the Church revolves around the Eucharistic sacrifice and the sacraments." (CCC 1113). But if, say, a baptism licitly performed by an ordained man is a liturgical action over which he presides, would not a baptism licitly performed by a lay person also be a liturgical act (if perhaps one of lesser solemnity) over which he or she presides? 1983 CIC 230.3 states ". . . lay persons can also . . . exercise the ministry of the word . . . preside over liturgical prayers . . . confer baptism . . . ". Emphasis added.
Or again, recalling that the sacrament of marriage is celebrated by the spouses, is not the Rite of Marriage itself (not to be confused with a wedding Mass) a very common liturgical action presided over by laity? And even if we were to focus on the official witness of a wedding (who is typically an ordained man per 1983 CIC 1108), are weddings officially witnessed by ordained men liturgies, while those officially witnessed by lay persons per 1983 CIC 1112 are not liturgies?
Obviously, certain liturgies can only be presided over by the ordained. Even in those liturgies that can be led by laity, however, ordained presiders, being more closely configured to Christ the High Priest, bring to their role a greater disposition for liturgical ministry, they offer a more perfect sign of our communion with one another under a hierarchic governance, and they are usually permitted a greater degree of solemnity in the celebration of the liturgy than are lay celebrants.
But I don't see how any of those considerations require one to hold that only the ordained can preside at any liturgy, unless, that is, the term "presider" is being understood tautologically as "an ordained leader of a liturgy", in which case, though, it adds nothing to our understanding of liturgical leadership, and risks blurring recent recognitions of legitimate lay leadership roles in certain liturgical actions.