To take the bashing off of one brother, I agree that I don't see the altar call as being commanded in Scripture. Baptism was to be the public profession of faith. Was throughout Acts. Altar calls are modern inventions.
The argument goes: they aren't condemned in Scripture, so why not? Neither are oil wrestling matches. Are these fair game for worship in the church? And I've heard the "hymnals aren't commanded/prohibited." stuff. Again, you're talking apples and apple computers. One is a practice (the altar call); the other is a conduit/facilitator for the practice (hymnals, electricity, etc.). This is fundamental. We shouldn't abuse the Word of God by falsely defining something. Singing is an element; psalms, hymns, songs are the conduits. That's why I get frustrated with those who say choruses are wrong. There's nothing to say that. But some choruses need thrown out because they're indicative of shoddy theology. So are some hymns. Whether we are regulative or normative, can we at least agree that a practice must adhere to Biblical principles (and not violate them)?
Far too many preachers make the altar call an essential element of a gospel response. This is Scripturally unfounded. Repentance and faith are these responses, with baptism being the public confession.
The practice itself is not commanded to be part of worship. Singing, prayers, preaching, offerings, ordinances...these are. I think when we really think through our theology of worship and the theology of salvation, we have some 'splainin to do when we tack on this modern invention.
There has been a good summary of the normative vs regulative principle. It boils down to that. Those who hold to the regulative principle would see the altar call differently than the normative principle adherents.
Now, I give invitations. You have to nowadays in the Baptist churches. You can preach that Jesus is a woman, but as long as you give an altar call you're okay in most so-called Baptist churches. Sometimes you have to remember that churches are not born where they need to be. I do my dead level best to articulate clearly that the person making a public response is doing so to only share what has been wrought in their hearts, but never so much emphasis that the act of baptism is diminished (the altar call has pretty much castrated the act of baptism in most Baptist churches ironically) or that the fruit of a changed life is not made second to the emotional "I went forward I was so moved today" appeal. I agree that abuses should not make us jettison a practice. The ultimate test of whether we practice something or not in worship is does this pass a Bibilcal litmus test.
Even anti-altar call folks had some sort of public response as part of their church ministry. Spurgeon had inquiry rooms, for example. We need to remember that some of the greatest men of God and most fruitful evangelists never gave an altar call. Lloyd Jones, Spurgeon, Whitefield, etc., and a host of contemporary folks all don't have an invitation hymn, yet people run to the cross for salvation and they appeal for them to do so.
I realize this is a sacred cow. I realize emotion takes over. But I encourage all to examine their theology of worship and their soteriology. Look at the altar call (or anything) through a Biblical lens. Leave off what granny said and brother so-and-so did, and let God's word ring true. You might be surprised.