Evil is -at its core -that which adversely affects a system which is beneficial -and a person is evil when they will to do so.
The intentions of a person make them good or evil, but the overall results of their actions make the actions good or evil.
As has been said, the road to hell is paved with good intentions.
Believers and non-believers are both subject to making mistakes due to ignorance of the overall nature of the system they are within.
The more capable and knowledgeable we become, the greater the potential for evil.
A believers' mindset might adversely affect others by their closed-mindedness causing people to be ignorant of certain things, and to not accept things which are beneficial, but the capabilities made possible by scientific discovery can lead to a corruption of -or the complete destruction of -all life on earth -even by accident.
A religious belief might keep one from accepting beneficial medical advancements made possible by science, but those same advancements can also lead to horrible tragedies due to a mix of knowledge and ignorance.
For example..... We are altering, and even synthesizing, DNA without a complete knowledge of the implications. The science that allows for plants that glow in the dark when they need water -are resistant to certain diseases, etc., might have some short-term benefits, but potentially cause even greater long-term problems. Some fear that synthetic DNA might escape somehow and cause all sorts of problems -and we don't know that it will not.
I don't even want to think about the possibilities given present knowledge coupled with an evil mindset**.
The splitting of the atom led to a situation which may very well destroy all human life, at least -and that may even be a better alternative than an abominable state caused by messing with DNA.
Ignorance can be a good thing when accurate vision and discipline are lacking.
From a biblical perspective, the present state of affairs is known as eating from the tree of the knowledge of good and evil.
Eating from the tree of life only would have meant continual guidance and government by God -so that we might have protection from forces greater than ourselves, avoid causing many of our own maladies and then seeking remedies, and make advancements in balance with the overall system of which we were initially ignorant.
In other words, we could have advanced more quickly without any risk of destroying everything and ourselves.
After the events in Eden, God purposefully allowed mankind to make their own choices, but also made choices for them which would manage risk and bring them to the end declared from the beginning.
There was a plan for the possibility of obedience -and a plan B for (perhaps inevitable) disobedience (rejection of knowledgeable guidance) which would eventually completely eradicate the possibility of disobedience (and so... disorder leading to tragedy) by allowing us to learn from our choices while managing the risk.
For example... confusing man's speech at Babel postponed the state of affairs we see today for thousands of years while other things were accomplished.
We will now be allowed to nearly destroy all life on earth -but a complete destruction will be prevented.
We will then have a collective experience base from which to discern that obedience to -and government by -God and Christ (belief in him will be made much easier by his actual presence) is necessary.
Mat 24:21 For then shall be great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be.
Mat 24:22 And except those days should be shortened, there should no flesh be saved..............................
**"It's interesting - I used to have this professor at Oxford, okay? Doctor Wickham, his name was and he was, like, this massive fat guy, you know? Huge, big guy. We used to call him - you know, well, I won't tell you what we used to call him, but he taught biomolecular kinetics and cellular dynamics. And he used to sort of scare the underclassmen with this story about how the world would eventually be eviscerated by technology. You see, it was inevitable that a compound would be created which he referred to as the 'Anti-God'. It was like an accelerated mutator or sort of, you know, like a, an unstoppable force of destructive power, that would just lay waste to everything - to buildings and parks and streets and children and ice cream parlors, you know? So whenever I see, like, a rogue organization willing to spend this amount of money on a mystery tech, I always assume... it's the Anti-God. End-of-the-world kinda stuff, you know... But no, I don't have any idea what it is. I was just speculating."