Why do people think that the concept of religion and God is a problem? I understand that many evil examples by apparently religious persons have turned people away. Still, I don't fully understand why they think it's something that needs to be eliminated.
"He who walks in his uprightness fears the LORD, but he who is devious in his ways despises Him" (Proverbs 14:2).
Few people enjoy having their flaws pointed out. They would much rather pretend there are no flaws. If that doesn't work then these people will attack what is showing their flaws to claim that the messenger is the one actually the one in the wrong.
The wicked desire to control their own lives. They don't want anyone or anything telling them what they can or cannot do. "Yet in the same way these men, also by dreaming, defile the flesh, and reject authority, and revile angelic majesties" (Jude 8). The very idea that there is a standard above them to which they are held accountable gives them nightmares. Thus, any code of belief that holds standards they find unacceptable is ridiculed and removed.
The wicked believe they are superior but Christianity teaches us to be humble and serve our fellow men. "He who despises his neighbor sins, but happy is he who is gracious to the poor" (Proverbs 14:21). Those given over to evil lie to themselves about their own importance. Thus, when they run across people who don't support their view, everything about them has to be destroyed. The confidence of righteous people in their God and His teachings is a barrier to the wicked's view of his own greatness. (Proverbs 14:26-27). Their arrogance can't allow them to ignore the righteous -- they have to destroy it so that they can continue to tell themselves they are great. Haman exemplifies this in Esther 3:5-6; 5:11-14.