Don't you think it could make someone leave a carefree life and
continue to live in sin because Jesus has already paid for it, the
present, past and even the future sin?
The answer is "No."
Of course, the born again saints also commit sins for the rest of their lives. But they can't sin willfully because the Holy Spirit dwells in their hearts. Actually, they become more sensitive to every sin after being born again. They come to know that they are the ones who cannot but sin until they die, and that the only way to avoid the chances of sinning is to serve the righteousness of God, that is the gospel of the water and the Spirit. In short, the Holy Spirit in them lead them to do God's work first apart from the lust of the world.
At the age of the Apostles, it seemed that they asked the same question
to the Apostles. So, the Apostle Paul said, "What shall we say
then? Shall we continue in sin that grace may abound? Certainly
not! How shall we who died to sin live any longer in it? Or do you
not know that as many of us as were baptized into Christ Jesus were
baptized into His death? Therefore we were buried with Him through
baptism into death, that just as Christ was raised from the dead
by the glory of the Father, even so we also should walk in newness
of life" (Romans 6:1-4).
Again he said, "What then? Shall we sin because we are not under
law but under grace? Certainly not! Do you not know that to whom
you present yourselves slaves to obey, you are that one's slaves
whom you obey, whether of sin leading to death, or of obedience
leading to righteousness? But God be thanked that though you were
slaves of sin, yet you obeyed from the heart that form of doctrine
to which you were delivered. And having been set free from sin,
you became slaves of righteousness" (Romans 6:15-18).
The person who is REALLY born again of water and the Spirit cannot sin more than before. Rather, he/she is rejoicing over the gospel everyday, and tries to preach it all over the world. In other word, he/she became a person who seeks first the Kingdom of God and His righteousness earnestly by the Holy Spirit (Matthew 6:33).