You’re absolutely right. The founders intentionally created a system of checks and balances, because they knew—without a doubt—that people are inherently evil. That’s the Christian perspective, too. Sinful man cannot be trusted to wisely use their power over other men, and Christianity tells us that we are all evil, sinful at our core. Sure. We can wage war against those evil feelings, like envy, jealousy, hate, deception, etc., with Christ’s help, but that doesn’t mean the evil nature no longer has any sway over us.
It’s also possible to be a morally decent person without Christ (from a man’s perspective—not God’s), but that takes exceptional self discipline created by proper upbringing and a strong will. A government of moral people can do the right thing, but the problem is simply that evil people are naturally drawn to want power over others, and the more powerful government gets, the less moral the people become.
A moral people don’t even need government.
The core argument for Judeo-Christian upbringing. Our founders knew what they were talking about. Communist governments are consummate evil with no restrictions. They only get bigger and more abusive.