I am not against altar calls as a method of calling for repentance in certain situations. I will admit that sometimes altar calls are good and proper. Likewise, I don't think that everyone who gives an altar call is necessarily omitting the Gospel call in their preaching.
I am against the thinking that views the altar call as always being necessary in order to have effectively presented the Gospel, a la Ergun Caner. It is the Spirit working through the preached Word that brings life. Life doesn't happen at the 'front', 'altar', or 'mourner's bench'. Life happens as the Word takes root in a person's heart. The response then is not a walk to the front to display ourselves to the congregation, but a change in our daily living.
My main problem with the altar call is that we seem to be training people to look at themselves intently as in a mirror, and then sending them on their way to forget about what they have seen. We have very good listeners to the Word, but not many doers. There are two remedies to this;
1) Stop sending the wrong message to them. The altar call gives the perception that all that the Gospel requires of us is a trip to the front to converse with the preacher. This is not a proper response to the Gospel. The Gospel requires a new way of living. The Gospel is message to be believed, but it is also a life to be lived. This demand is upon believers and unbelievers alike.
2) Teach them how to hear and respond to preaching. Preaching is not a fast food meal. It is a seven course meal that must be digested and all of the minerals put to use. We must learn to meditate on the message. We must become Bereans, searching the Scriptures to see if these things are so. Our response to preaching is not so trivial that we can respond without any thoughtful deliberation. We must ask diagnostic questions of the message and ourselves. This cannot be done in a fifteen minute session with the preacher, but must take place throughout the week as the Spirit will call these messages to memory and continually apply them to our lives, creating faith and repentance, and growing us in sanctification.
Here's a great article that really gets to the heart of the matter.