Paul is on a roll. Having just, well, whined about his mistreatment by the brethren, he now wants them to all join hands, sing kumbayah, and toss some immoral people out of the church.
As John F. Kennedy used to say, "Let me say this about that":
1. Paul doesn't expect the world to be holy. In modern terms, he's not trying to ban gay marriage in Montpelier, he's trying to stop divorce in the local church.
2. This isn't like forcing other people to not smoke because you oppose smoking and you have the votes. This is protecting myself from the secondhand smoke of someone else's sin. You wanta smoke? Take it outside. Nothing personal, but you are not welcome here if you insist on making the rest of us sick. Make no mistake, sin is a contagious disease, Paul says. Let a little bad yeast work through the dough, and pretty soon it all tastes like, well, spoiled food.
The offending sinner may feel offended. "Don't you love me? Aren't you being intolerant?" He may even threaten to sue! Well, brother, I am offended at your offense, that you would think I love coddling your feelings more than I love Christ or the spiritual welfare of these little ones. When you're tired of eating corn pods with the pigs I will be the first one to run out and greet you, throw a robe around you, and welcome you back.
3. Paul focuses on sexual sin, but at the end of the passage says that greedy, idolatrous etc. also should get this treatment too. I think the modern American church might practice less selectivity on the sins it condemns. On the sins. The sinners themselves are always welcomed back.
Oh, this is a tough subject. Even "getting it right" on paper is really tough, I'm sure I haven't touched all the bases. Walking it out is torture. How easy to toss off a few words in a blog and be done with it. God bless the elders who have to actually expel those they love.