Are denominations a winnowing process?

for there must be factions among you in order that those who are genuine among you may be recognized (1 Cor 11:19).

i) Ecumenists lament denominations. However, this verse raises the question of whether denominations are, in fact, necessary. 

ii) Some commentators think the verse must be ironic. Surely Paul can't say anything good about factions. Hasn't he been attacking factions within the church?

iii) Keep in mind that there's nothing in the wording of the verse itself to indicate that Paul is speaking ironically. Unless we think Paul can't be serious, there's no reason to reach for the ironic interpretation.

iv) To say that Paul thought factions are bad is simplistic. For instance, it depends on which side of the dividing line you're on, and how you got there. For one thing, you might have two (or more factions) because one group broke away from another. It's not that all parties concerned are divisive. If one group breaks ranks with another, that leaves two factions–but not because both were necessarily divisive. Rather, one group separates from another while the other group finds itself separated–as a result of the group which initiated the split. "We didn't leave you–you left us!"

You can also have factions because one group expels another group. That's different than one group splitting from another.  

Likewise, there are situations in which it may be necessary to break away. OT prophets often stood apart from the religious establishment. As did John the Baptist. As did Jesus. As did Paul himself. So it depends on whether one has just case. Even if factionalism is blameworthy, that doesn't entail that each party is blameworthy.

v) Division can be a winnowing process. Sifting the wheat from the chaff. The Bible often uses that type of metaphor. As one commentator observes:

Although this could possibly be irony…more likely it is a reflection of Paul's "already/not yet" eschatological perspective (see on 4:1-5). 

In keeping with the teaching of Jesus [Mt 10:34-37; 24:9-13], Paul expected "division" to accompany the End, divisions that would separate true believers from those who were false…Paul, therefore, probably sees their present divisions as part of the divine "testing/sifting" process already at work in their midst…God is working out the divine purposes; those who truly belong to God, the "tested/approved" (dokimoi=those who have passed the "examination"), are already being manifest in their midst, and presumably they will escape the final judgment that is coming upon the world (v32). G. Fee, The First Epistle to the Corinthians (Eerdmans, rev. ed., 2014), 596-97.