That's all nonsense. You can't just pull a verse and take it out of context. You have to look at the verses on either side to fully determine its meaning.
(Joel 3:9-16 NIV) Proclaim this among the nations: Prepare for war! Rouse the warriors! Let all the fighting men draw near and attack. {10} Beat your plowshares into swords and your pruning hooks into spears. Let the weakling say, 'I am strong!' {11} Come quickly, all you nations from every side, and assemble there. Bring down your warriors, O LORD! {12} 'Let the nations be roused; let them advance into the Valley of Jehoshaphat, for there I will sit to judge all the nations on every side. {13} Swing the sickle, for the harvest is ripe. Come, trample the grapes, for the winepress is full and the vats overflow-- so great is their wickedness!' {14} Multitudes, multitudes in the valley of decision! For the day of the LORD is near in the valley of decision. {15} The sun and moon will be darkened, and the stars no longer shine. {16} The LORD will roar from Zion and thunder from Jerusalem; the earth and the sky will tremble. But the LORD will be a refuge for his people, a stronghold for the people of Israel.
You can't simply be a sinner and proclaim yourself righteous. Those of us who are saved are covered by the righteousness of Christ:
(2 Corinthians 5:17-21 NIV) Therefore, if anyone is in Christ, he is a new creation; the old has gone, the new has come! {18} All this is from God, who reconciled us to himself through Christ and gave us the ministry of reconciliation: {19} that God was reconciling the world to himself in Christ, not counting men's sins against them. And he has committed to us the message of reconciliation. {20} We are therefore Christ's ambassadors, as though God were making his appeal through us. We implore you on Christ's behalf: Be reconciled to God. {21} God made him who had no sin to be sin for us, so that in him we might become the righteousness of God.