1Joh 1:8 is presented within the context of one having a criminal record before God, not in the context of ongoing criminal activity against God.
John is writing to people that they may be cleansed of all sin and unrighteousness through the shed blood of Jesus Christ. In order to be cleansed one has to come clean before God. We see this evidenced in passages like this...
1Jn 1:7 But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin.
1Jn 1:8 If we say that we have no sin, we deceive ourselves, and the truth is not in us.
1Jn 1:9 If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
1Jn 1:10 If we say that we have not sinned, we make him a liar, and his word is not in us.
In passages like this...
Heb 10:19 Having therefore, brethren, boldness to enter into the holiest by the blood of Jesus,
Heb 10:20 By a new and living way, which he hath consecrated for us, through the veil, that is to say, his flesh;
Heb 10:21 And having an high priest over the house of God;
Heb 10:22 Let us draw near with a true heart in full assurance of faith, having our hearts sprinkled from an evil conscience, and our bodies washed with pure water.
As well as in verses like this...
Pro 28:13 He that covereth his sins shall not prosper: but whoso confesseth and forsaketh them shall have mercy.
Even Isaiah wrote...
Isa 55:7 Let the wicked forsake his way, and the unrighteous man his thoughts: and let him return unto the LORD, and he will have mercy upon him; and to our God, for he will abundantly pardon.
Yet despite the clarity of these Scriptures, if one is to contend that one actually has to forsake all known unrighteousness and be a doer of righteousness, then many religious folk who proclaim to believe in Jesus will oppose such one who contends such a thing.
Why are you in opposition to a ceasing from all known evil and a wholehearted yielding to God Blain?
The Bible clearly teaches that mercy is granted AFTER a repentance which is inclusive of the forsaking of evil. In other words if one refuses to forsake all known evil then that one has not yet found mercy/forgiveness.