If you are asking this question, regardless of which side you agree with, you do not know or understand the scriptures. The Bible, Book of Mormon and Doctrine and covenants all agree that it is not possible for a person who is truly born of God to "sin" because like little children, they are not "capable of committing sin".

For example, here's one of the ways the Bible says it:

9 Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God.

This isn't a one off verse, its a repeated theme mentioned by over 15 separate authors in 20 distinct books of scripture, across at least 27 passages totaling over 52 verses. It is indirectly supported or relied upon by even more authors in an additional 200+ verses.

(Don't confuse not being able to sin with being perfect. Those definitions don't match up in the scriptures. And you can make mistakes without those mistakes being called sin.)

Here's the logic the scriptures teach:

1) The law is required to sin. Without the law, there is no sin. Sin is to break the law of God. (10 Commandments for example)

2) Little Children are not under the law, they are alive in Christ = Cannot sin. No matter what they do, it is not counted as a sin, even when it is not good or right or the best thing. They are innocent and learning, growing and developing. They are like Adam and Eve in the Garden who learned from their own experience to distinguish good from evil.

3) Just as Adam and Eve fell, little children also fall and are given the law at which point they become sinners. The scriptures call this the Preparatory Gospel which holds the keys to "the law of carnal commandments" and is administered by the Aaronic priesthood. The Aaronic priesthood does not have power or keys to administer anything else except the Preparatory Gospel and its law of carnal commandments, (D&C 84:25-27).

4) Anyone who is under the Preparatory Gospel is under the law and is a sinner. They are "judged by their works", (D&C 76:109,111), which ultimately can't save them. They are Telestial and receive a reward for their works which is why this kingdom is like the stars where every start is different is brightness with unlimited possibilities.

5) When we are truly converted to Christ, we are given the Holy Spirit and the law is taken away or removed. Without the law, we cannot sin and there is no punishment, (which is the point of being saved), we are "alive in Christ". We can't sin because the law is taken away and sin requires a law to break. We have "become like little children" again. We are saved from the fall and brought back into a garden like state that Adam and Eve were in before they fell. These are Terrestrial who "died without the law", (&C 76:71-72). We are no longer under the Aaronic Priesthood, we are now under the Melchizedek Priesthood which does not administer a law, but administers the spirit. The Spirit tells you all things that you should do even at times to break the old law.

6) The scriptures don't say the Law ended for everyone. They say some people are under the law still and some are not. They use conditional words like "If" you meet this criteria, then you are not under the law implying that "If" you do not meet that criteria, then you are still under the law. for example:

18 But if ye be led of the Spirit, ye are not under the law.

Here are a few more of the many references to these concepts:

Sin requires a law:

17 Now, how could a man repent except he should sin? How could he sin if there was no law? How could there be a law save there was a punishment?

15 Because the law worketh wrath: for where no law is, there is no transgression.

Behold, my son, this thing ought not to be; for repentance is unto them that are under condemnation and under the curse of a broken law.

12 For as many as have sinned without law shall also perish without law: and as many as have sinned in the law shall be judged by the law;

When we are converted, the Law is removed:

23 But before faith came, we were kept under the law, shut up unto the faith which should afterwards be revealed.

24 Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith.

25 But after that faith is come, we are no longer under a schoolmaster.

27 Wherefore, we speak concerning the law that our children may know the deadness of the law; and they, by knowing the deadness of the law, may look forward unto that life which is in Christ, and know for what end the law was given. And after the law is fulfilled in Christ, that they need not harden their hearts against him when the law ought to be done away.

Concepts like Law, Sin and Punishment are only relevant to people under the law

19 Now we know that what things soever the law saith, it saith to them who are under the law:

14 For sin shall not have dominion over you: for ye are not under the law, but under grace.

25 Wherefore, he has given a law; and where there is no law given there is no punishment; and where there is no punishment there is no condemnation; and where there is no condemnation the mercies of the Holy One of Israel have claim upon them, because of the atonement; for they are delivered by the power of him.

Here here are a few places where the Book of Mormon says after we are converted to Christ, we become like little children who cannot sin.

25 Wherefore, he has given a law; and where there is no law given there is no punishment; and where there is no punishment there is no condemnation; and where there is no condemnation the mercies of the Holy One of Israel have claim upon them, because of the atonement; for they are delivered by the power of him.

22 For behold that all little children are alive in Christ, AND ALSO all they that are without the law. For the power of redemption cometh on all them that have no law; wherefore, he that is not condemned, or he that is under no condemnation, cannot repent; and unto such baptism availeth nothing—

23 But it is mockery before God, denying the mercies of Christ, and the power of his Holy Spirit, and putting trust in dead works.

24 Behold, my son, this thing ought not to be; for repentance is unto them that are under condemnation and under the curse of a broken law.

In the following passages, John and Mormon are saying the exact same thing but using their own words:

6 Whosoever abideth in him (Christ) sinneth not: whosoever sinneth hath not seen him, neither known him.

7 Little children, let no man deceive you: he that doeth righteousness is righteous, even as he is righteous.

8 He that committeth sin is of the devil; for the devil sinneth from the beginning. For this purpose the Son of God was manifested, that he might destroy the works of the devil.

9 Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God.

10 In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother.

6 For behold, God hath said a man being evil cannot do that which is good; for if he offereth a gift, or prayeth unto God, except he shall do it with real intent it profiteth him nothing.

7 For behold, it is not counted unto him for righteousness.

8 For behold, if a man being evil giveth a gift, he doeth it grudgingly; wherefore it is counted unto him the same as if he had retained the gift; wherefore he is counted evil before God.

9 And likewise also is it counted evil unto a man, if he shall pray and not with real intent of heart; yea, and it profiteth him nothing, for God receiveth none such.

10 Wherefore, a man being evil cannot do that which is good; neither will he give a good gift.

11 For behold, a bitter fountain cannot bring forth good water; neither can a good fountain bring forth bitter water; wherefore, a man being a servant of the devil cannot follow Christ; and if he follow Christ he cannot be a servant of the devil.

This is what it means to become like little children

Matt. 18:3 (See also 3 Nephi 11:38)

3 And said, Verily I say unto you, Except ye be converted, and become as little children, ye shall not enter into the kingdom of heaven.

If you want to understand this better and see more of the scriptures that teach this, read this short book: