(1) I see no harm whatsoever in surrendering words to the fickle tides of usage, so long as we're willing to take the trouble to find new effective ways to express ourselves. The challenge to the Church is always to hit a moving target: to express the unchanging gospel in a language that is never the same. If we try to hold rigidly onto certain words, despite how others use them, we are doomed only to speak to ourselves. Remember the reformation debates over translating the Bible into the vernacular.1) I agree with your sentiment. When people start using a different language to express themselves, there is nothing wrong with taking their language. But Douglas Wilson's point isn't to win the culture (though if you read his other stuff, you see that too), but it's to have something to win the culture to. When the culture co-ops Christianity, then it's not time to leave the terms "evangelical" and "Christianity" behind, it's time to defend them so that the boundaries are clear that if the culture wants to come, it comes on God's terms and not theirs.
(2) Better to argue over doctrine than over labels for doctrine.2) When people start defining themselves as evangelical when they clearly are not, or, when people who call themselves evangelical clearly drift out of it, it becomes a matter of church discipline. If I called myself a Christian and started committing adultery, my church would be absolutely right in rebuking me and showing me to the door. Same thing if I start committing theological adultery. It's not the label as what is wearing it, and that's doctrine.
(3) But the fights Wilson talks about are not really fights over words---words like "Christian" or "evangelical". He's really talking about group-identification. His distress is that people who disagree with him (more or less radically) are calling themselves the same thing he calls himself. Perhaps he should change the usage he has control over--his own--rather than the usage he doesn't control? Annoying to have your trademark stolen, but these things happen. It's hardly on par with rape.3) This is a call for church discipline, and to the extent that the Church (capital 'C') disciplines its members, it controls the usage. To take an Old Testament example, if Israelites started one day to intermarry with Canaanites, is there warrant to discipline them out of the body of covenant believers? They are bearing God's name in vain.
Whether or not it's rape, it certainly is gross idolatry, which is spoken of as being on par with sexual immorality. As we stand by and watch as people in our churches do it to the church that Christ dies for it demonstrates a real lack of love, whatever we say. Thus the rape analogy. If I love someone, I stake my life on it.
(4) Unless he has something slightly stronger in mind. Could he be using these words as code for "the elect", "the brethren"? Then again, what's at issue is not the words, it's who belongs to this group, whatever it's called. And if that's what he means, I have even less patience. You may disagree strongly with the open theism, you may hate it, but is it even plausible that believing in open theism jeopardizes one's salvation? Does it contradict anything in the ancient creeds?4.1) The issue is "what group has the right to call itself Christian or Evangelical?" The answer is "the group that is composed of Christ-followers and are centered upon the Good News." When someone continues to use the terms but deny their very meaning, I'm not going to walk away without a fight. Tolerating someone take on the name of the Lord in vain is irreverent. Allowing someone to take it away from me is stupid.
4.2) You say "is it even plausible that believing in open theism jeopardizes one's salvation? Does it contradict anything in the ancient creeds?" and that's another thread. But let's take a basic example to allow me to express why I feel the same outrage at open theism. What if, in my response to your comment, I referred to you as a "she", assumed you were an undergraduate at Duke University (certainly not a bad school), were majoring in biology, and so on? Would you be offended? Would it be appropriate to consider myself in a close intimate relationship with you?
In the same sense that you could rightfully say that I wouldn't have a meaningful relationship with you if I didn't understand you to such an extent as to mistake your gender, your age, your school, your major, and a whole other slew of facts, I think open theism strikes at the very heart of the character of God, and thus is idolatry, worshiping a false God.
4.3) And when did disagreeing with an ancient creed mean false Gospel? Isn't false defined by disagreeing with the Bible? Were Arians worshiping a false God prior to the decree that Arians were heretics?
(5) We are not the border patrol of the Kingdom.5) I don't agree with you here at all, and I don't think you do either. If you truly believed what you were said, why did you post your comment? But isn't it your concern that the body of Christ represent itself as faithfully as possible that leads you to post what you write? For that I commend you and welcome the discussion. But if you think we shouldn't be having this discussion, then why post at all?