Another commenter, ostensibly gay, responded with the following wonderful observation: When is the last time you heard of someone being excommunicated because of his greed?
I have written you in my letter not to associate with sexually immoral people— not at all meaning the people of this world who are immoral, or the greedy and swindlers, or idolaters. In that case you would have to leave this world. But now I am writing you that you must not associate with anyone who calls himself a brother but is sexually immoral or greedy, an idolater or a slanderer, a drunkard or a swindler. With such a man do not even eat.
What business is it of mine to judge those outside the church? Are you not to judge those inside? God will judge those outside. "Expel the wicked man from among you."
That's an excellent question.
To be fair, it's arguably easier to identify sexual immorality than greed because scripture explicitly describes certain sexual practices as being sinful. That said, Paul still chooses to include "greed" in the list of offenses that can potentially require a congregation to break fellowship. So this begs the question: why the disproportionate emphasis on homosexuality?
In light of Paul's last command to the church in Corinth, shown above, it seems to me that the evangelical church in America may spend far too little time judging those inside the church and far too much time judging those outside the church.
Now, I happen to support the orthodox view when it comes to homosexuality. On the other hand, it also seems obvious that the church could do a better job of applying church discipline evenly, as it is described by Paul, and could expend a lot less effort decrying the faults of those outside the church.