do you really believe everyone who has ever been baptized is a Christian?
you do know infant baptism exists, and false teachers exist, and emotional peer pressure exists, right?
in the early church they would not allow people to be baptized until they had been taught - perhaps even for two or three years. part of this was making sure they were truly believing and understanding what they were doing, not just responding in the spur of the moment to a charismatic speech, and part of it also was because spies were sent in during times the church was being persecuted and meeting in secret.
how many people today are baptized and don't really know the gospel at all? we have traveling 'revival meetings' where hordes of money is raked in and people who have never heard the Bible preached at all are baptized on the spot. but is the gospel even being preached accurately in these?