I serve as the lead elder in a local church called Jubilee in St Lous and our eldership team was discussing the topic of spontaneous baptism. Should we encourage or allow people to be baptized spontaneously while we are batizing others that have thoughtfully considered it over a period of time? We went with the former. The decision that we (the elders at Jubilee) made to invite people to be spontaneously baptized was not a flippant decision. We had two main concerns: 1) We didn't want to push people into making an emotional decision without first allowing the Holy Spirit to work on their heart and 2) We didn't want to baptize someone who was not actually a Christian yet.
Concern 1: Emotionalism
I would define emotionalism as making a decision based on how you feel versus true conviction of the Holy Spirit. It's getting caught up in the moment versus getting caught up with God. Repeated and long alter calls could lend itself to emotionalism. However, understanding the dangers of emotionalism, we think calling people to respond immediately to God by being baptized is ultimately a good thing if we have first laid out clearly the gospel.
In Acts 8, Philip lays out a clear presentation of the gospel to the Ethiopian Eunuch using a passage from Isaiah. Seeing some water, the eunuch said, "See, here is water! What prevents me from being baptized?" The answer was clearly nothing as Philip baptized him on the spot.
Sometimes in our culture, people view baptism as something they need to work towards or earn rather than seeing salvation as a free gift and baptism as a symbol of that gift. It's helpful to show people that God's work in our life is based on Jesus' finished work and on our ongoing performance. We have come to the conclusion that inviting people to be baptized spontaneously is not founded on emotions but is a Biblical way of leading people through how they should respond to God's salvation.
Concern 2: Baptizing Someone Who Isn't a Christian
Another concern we had in doing spontaneous baptisms is we might unknowingly baptize someone who is not a Christian. This concern has led many churches to require classes before being baptized to make sure the people understand what they are doing and exactly what it means to be a Christian. While we think it is very important to teach people what Christian doctrine is and how to respond in light of that doctrine, we don't see that as being a prerequisite for salvation and baptism.
In Matthew 28:19-20 Jesus says, "Go therefore and 1) make disciples of nations, 2) baptizing them in the name of the Father and of the Son and of the Holy Spirit, 3) teaching them to observe all that I have commanded you..." In other words, 1) make them, 2) mark them and 3) mature them. Getting the order right is important. It doesn't say make disciples and then once they learn everything, baptize them. We are to mark them as disciples before they mature (in other words, before they act like Christians).
But it is important that they are first Christians. Before we baptize anyone, planned or spontaneous, an elder or deacon asks each person, "Have you repented and do you want to trust Jesus?" If someone says yes, regardless of their past, we must trust the Holy Spirit to work in their life. This is one of the reasons why Jesus gave us the parable of the weeds. In this parable (Matthew 13:24-30), the servants ask the master if they should get rid of the weeds that grow up alongside the wheat. The master said, "No, lest in gathering the weeds you root up the wheat along with them. Let both grow together until the harvest, and at harvest time I will tell the reapers, 'Gather the weeds first and bind them in bundles to be burned, but gather the wheat into my barn.'" In other words, it's not our job to judge and tear down what we think are weeds. If we do, we run the risk of uprooting good plants. This doesn't mean we don't ask questions and encourage people to respond in faith to what they now confess, but it does mean that we don't withhold baptism to someone who repents in their heart and confesses with their mouth that Jesus is Lord.
I hope that you and your eldership can find your way through this issue. We have found it to very helpful in not only seeing more people baptized, but it has raised the faith for salvation.