Somebody actually posed that question to Fr. Z.
The good padre — who was last heard from tackling the subject of deacons and the collar – offers an answer and some history.
Sadly, many permanent deacons I have known in times past were little more than glorified EMHC’s (Extraordinary Minister of Holy Communion) because they were lacking in good theological preparation before ordination. I am glad to hear far and wide that programs of formation for the permanent diaconate are being overhauled and vastly improved.
That said, a deacon is an ordinary minister of Communion, not merely an Extraordinary Minister of Communion, because of their ordination. Diaconate, after all, is a step of Holy Orders, which conforms their souls for the tasks to which Holy Church sets them.
We make a distinction between Ministers of the Eucharist and of Communion. The former confect the Eucharist. The latter distribute the Eucharist. Deacons don’t confect the Eucharist. Cf. Redemptionis Sacramentum 154.
This has roots, of course, in Scripture.
Read the rest, and take time to look over the comments, too, which are always interesting — and sometimes even entertaining.