I came across an interesting idea and though I would share it with the group:

"I’ve just found out about this great story from The Feethinker (thanks Joe!). Apparently, in just the last week alone, 1500 people in Britain paid for Certificates of Debaptism from the National Secular Society! Indeed, this has prompted Religious Intelligence to run a poll asking if Anglicanism should provide a service for people to annul their baptism (as Rome already does, apparently) - be sure to cast your vote! The atheist movement really is starting to gather strength across the world, isn’t it?"

I believe, and could be wrong that baptismal records can sometimes be used as proof of citizenship, so if you were to have all records of your baptism destroyed, that might be the only downside.  That aside, whether you get a certificate of debaptism or not, if you do have all records of your baptism removed, I think it would send a strong message.