The sentence "if God is so good, why..." often ends in one of two completely contradictory statements. The first is a question about why God doesn't stop evil. The second is a complaint about a time when He did. For example, the nations Israel destroyed were so evil, they burned their children alive as sacrifices to Molech, yet atheists complain about how God wiped them out. These same people ask why God allowed Hitler to carry out the Holocaust. So, when God judges sin, He's evil. When God doesn't judge sin, He's evil. Either way, atheists say God is evil.
Thinking it through logically, however, the better argument would be why does God stop some evil and not others? But even this has an answer. In short, it comes down to His infinite wisdom and authority. God has a plan, and He knows how to achieve it. In the end, all evil will be judged. That doesn't just mean the large evils, such as Communism, but also the small evils, like the ones you have committed. Whether God judges evil now, or temporarily refrains from doing so, the fact is you are evil, and therefore He has a choice. He would be quite within His rights to condemn you forever right now, but He can also choose, as He did, to nail all your sins to the cross. Your sin must be judged. The question you need to ask is who you want to bear that judgment. Yourself, or Jesus?