Summary: Sin, whether secret or public endangers not only the individual but those around as well. A person, a family, a community, a nation can fall under the curse of sin with grievous consequences. Abstain from all appearances of evil!
But the children of Israel committed a trespass in the accursed thing: for Achan, the son of Carmi, the son of Zabdi, the son of Zerah, of the tribe of Judah, took of the accursed thing: and the anger of the Lord was kindled against the children of Israel. Joshua 7:1
Israel hath sinned, and they have also transgressed my covenant which I commanded them: for they have even taken of the accursed thing, and have also stolen, and dissembled also, and they have put it even among their own stuff. Therefore the children of Israel could not stand before their enemies, but turned their backs before their enemies, because they were accursed: neither will I be with you any more, except ye destroy the accursed from among you. Up, sanctify the people, and say, Sanctify yourselves against to morrow: for thus saith the Lord God of Israel, There is an accursed thing in the midst of thee, O Israel: thou canst not stand before thine enemies, until ye take away the accursed thing from among you. Joshua 7:11-13
The sons of Judah; Er, and Onan, and Shelah: which three were born unto him of the daughter of Shua the Canaanitess. And Er, the firstborn of Judah, was evil in the sight of the Lord; and he slew him. And Tamar his daughter in law bare him Pharez and Zerah. All the sons of Judah were five. The sons of Pharez; Hezron, and Hamul. And the sons of Zerah; Zimri, and Ethan, and Heman, and Calcol, and Dara: five of them in all. And the sons of Carmi; Achar, the troubler of Israel, who transgressed in the thing accursed. And the sons of Ethan; Azariah. 1 Chronicles 2:3-8
Achan took what God forbade. Achan hid the accursed thing in his tent and brought a snare not only into his life but also into his family's life. What he did affected the performance and success of the whole camp, and resulted in an ignominious defeat from what should have been an easy victory.
Sin is an accursed thing in the sight of God. Its abhorrence to God is obvious in the fact that Jesus had to die on the cross for our sins, being made a curse for us.
Christ hath redeemed us from the curse of the law, being made a curse for us: for it is written, Cursed is every one that hangeth on a tree: That the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith. Galatians 3:13-14 KJV
The Word of God says that we have been redeemed from the curse through Christ's sacrifice but we need to be circumspect in our walk or:
WE WILL PROVOKE THE CURSE WHEN WE ENTERTAIN THAT WHICH GOD FORBIDS
Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness, Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God. Galatians 5:19-21 KJV
Now therefore there is utterly a fault among you, because ye go to law one with another. Why do ye not rather take wrong? why do ye not rather suffer yourselves to be defrauded? Nay, ye do wrong, and defraud, and that your brethren. Know ye not that the unrighteous shall not inherit the kingdom of God? Be not deceived: neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor abusers of themselves with mankind, Nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners, shall inherit the kingdom of God. 1 Corinthians 6:7-10 KJV