Then how does the congregation know that you screwed up?
They may or they may not. For that matter, you may or may not know you screwed up. Think about it.
Do you know that there are some people today that teach their children that there is absolutely nothing wrong with pre-marital sex? Do you know that there are some people today that teach their children that there is absolutely nothing wrong with homosexuality? Do you know that there are some so-called churches that teach the same exact thing? Do you know that the majority of public schools teach that same thing and penalize students who advocate a different position? As a consequence, you might have such a person who has never been taught that it is wrong. In these days, that is likely not all that uncommon any more (think about all of those people who are "spiritual," but not "religious")
You have got to teach those people, not condemn them. Faith comes by hearing. Hearing is really difficult if you're locked out.
One of you all cited 1 Cor 5:11 earlier, but you neglected to make reference to the context of that verse. 1 Cor 5:1-2a says, It is actually reported that there is immorality among you, and of a kind that is not found even among pagans; for a man is living with his father's wife. And you are arrogant! Ought you not rather to mourn? Note that it talks about immorality among you (i.e., there are people who are in the Church who are living in this kind of condition...and the church is bragging about it and lifting them up as examples)
Context makes all the difference, as the context of the verse talks about immoral conduct going on within the Church and among believers, not whether or not somebody as an individual is a sinner. Likewise, you'll find that the remaining verses that talk about excluding people talk about excluding disruptive people who try to lead people astray. None of them, particularly when you look at their context, talk about excluding people for their sinfulness in of itself.
The equivalent today is not simply allowing a prostitute, a democratic politician, or an abortionist to go to Mass. The problem is if the Church allows the prostitute to ply her wares at the Church picnic or allows the abortionist to advertise in the church bulletin (or hand out business cards after Mass), or allows the democrat to campaign.
The problem with the Church in Corinth was not that they admitted sinners, but that the Church endorsed the behavior and was bragging about it. ("See how open minded we are?") St. Paul is rebuking them on this because he doesn't want these folks to lead others astray (i.e., scandal).
One of the biggest issues in my church is high profile pro-abortion politicians receiving communion. Note: this is not to say that there is any outrage at these people being allowed to attend a Mass, but that they receive communion: there is a difference. I will explain in a minute.
My church, as you well know, does not have open communion (unlike many of them out there). In order to receive communion in my church, you have to be a member of my church or one that is in communion with my church and you have to be in a state of grace (i.e., you have to have confessed and been absolved from any serious sins). The reason for this is not in order to exclude anybody, but for the good of the person receiving communion (1 Cor 11:27 -29: Whoever, therefore, eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty of profaning the body and blood of the Lord. Let a man examine himself, and so eat of the bread and drink of the cup. For any one who eats and drinks without discerning the body eats and drinks judgment upon himself.)
So it's pretty much between the individual communicant and God: the communicant needs to examine his own conscience to determine if he is in a state of grace.
The issue with pro-abortion politicians receiving communion is one of scandal: there is a concern that their receipt of communion might be seen as an endorsement of their actions by the Church, thus allowing some to be led astray. If it wasn't for that, it would be up to the individual politician to examine his or her own conscience before approaching communion. (This will be hopefully coming to a head in a couple of weeks at the next bishops' conference meeting btw)
I could picture the same thing with a Tiller-like person. If such a person was to start bragging that he was a good Catholic who attended Mass every week at Saint Gianna Beretta Molla Catholic Church (a good Catholic will appreciate the irony there) and made sure to have lots of photo-ops of him receiving communion on his web site, I would hope that he would be instructed not to receive communion any more until he gave up the abortion business. Likewise, if anybody was to attempt to use the Church to advocate immorality, I know that this person would be reproved and instructed to stop it (and if they refused to do so, other steps would be taken to ensure that there was no ambiguity). But I can't picture any circumstance where a person would be excluded from attending Mass in of itself, provided that they behave themselves during the Mass.
That is different than the scandal that this Lutheran Church brought on themselves by allowing him to usher (as opposed to just attending their worship service) and, apparently, they have not only tacitly endorsed his behavior, they have actually endorsed it (via their prayer vigils after his death). Totally different situation.
But excluding a person from attendance at a worship service, in of itself, seems somewhat pharisitical on the surface. But that's not my business: your church can operate however it wants. As I said in my original post, my response is that I'm glad that I am not a member, as I doubt that I'd be welcome.