I disagree, in my interpretation of the Bible and Christianity (from when I was a Christian). I think you can't have good without evil, and vice versa (without comparisons and opposites, things "just are"--hot wouldn't be hot if there were no cold, for example), but my main point is that evil was created to test people, and so that they'd have free will. So, you have a choice.

Now, I also agree that many things that are meant for good are used by bad and evil people for evil purposes. But I don't think evil was created by those people, demons, The Devil, or whomever you want to claim did. The Bible says God created everything--including evil.

In Isaiah 45:7, it says:

I form the light, and create darkness: I make peace, and create evil: I the Lord do all these things