Scripture tells us why the office of deacon was created in Acts 6. There were squabbles between Hellenistic and Hebrew Christians over the care of those in need. The apostles said, “It would not be right for us to neglect the ministry of the word of God in order to wait on tables.” So they directed the congregation to pick seven men; the apostles said, “We will turn this responsibility over to them.” Clear, isn’t it? These folks don’t think so.
Yes, deacons have a liturgical role in distributing communion (and, in many Protestant churches, taking up the offering). But their primary role is to do the social ministry of the church. That’s why the office was created. It is their job to visit the sick, feed the hungry, distribute clothes–all the things needed to take care of brothers and sisters in need.
Advent Hope 
Fr. Z usually has good points, but he’s so pedantic and repetitive that I usually just skim his blog for actual news articles. Furthermore, I agree with you; I think he’s wrong here.
But, I think his is an overreaction to a historical overreaction. The reinstitution of the permanent diaconate has more often than not resulted in deacons who know little theology and do less service; they’re often older men from the local congregation, and it’s treated as a “status” thing as much as anything. When they’re at Mass, they stand up there and don’t look too sure of what they’re doing. (I know several good deacons who do lots of service and know what they’re doing at Mass, but they’re not the norm.)
So, I think Fr. Z is reacting to what’s clearly a wrong—an ignorant deacon who is little more to the church than liturgical furniture. But I also think he’s wrong himself—the deacon has a clear extraliturgical role in the way both Scripture and the “Aggiornamento” intended. It’s a role that, in today’s age of precipitously declining numbers of priests and religious, makes a lot of sense if done properly.
Deacons in parts of the US are the only native clergy, they are formed to see themselves as para-presbyters rather than deacons. The fact that married men can be ordained deacons but not presbyters means that many married men who seek ordination into the former really feel called to the latter.
Interestingly, of the top 5 deacons I know, 2 are unmarried, 1 is a widower, and 2 are transitional.