As a guy who was baptized as a baby (and who feels quite often like a filthy casual of a Christian lol), I would say no, they shouldn't be baptized again. Ephesians 4:4-6 says: "4 There is one body and one Spirit, just as you were called to one hope when you were called; 5 one Lord, one faith, one baptism; 6 one God and Father of all, who is over all and through all and in all."
The reason I don't like the whole re-baptism thing, is because it assumes that something was wrong with the first baptism, or that the first one didn't work or do anything. Baptism is supposed to be for the remission of sins, the regeneration of the spirit, the uncovering of the Image of God within each of us, our death to ourselves and resurrection to new life in Jesus, and admittance into the Church. Now, if you believe your first baptism did all those things, except now you live for yourself and not for Jesus, does that mean that you should be baptised again? In my view, no--repentance is a lifelong process, not something that is completed in an instant, so of course we'll still slip up after baptism.