i do believe in God. and yet there is also extreme evil in the world.
if you believe in the God described in the Bible, it's pretty inconsistent not to believe in opposing forces of good and evil. and of course the Bible speaks about both angels and demons. i think that there are both people who underestimate and others who overestimate the activity of either or both angels and demons. i don't attribute all bad stuff in the world to demon activity, but i do think that in some cases that is not only possible but probable.
some bad stuff just comes from the fact that all of us have a human nature that is capable of doing right or wrong. and far too often, humans choose wrong - what the Bible calls sin. hard for any of us survivors to deny that one - whatever you want to call it. and ultimately - all evil, sin and bad stuff can be traced back to going against God - whether it is Satan, demons, sin or human nature.
that's how i see it.
"My experience has shown me that I all too often tend to deny that which lies behind, but as I still believe, that which is denied cannot be healed." Brennan Manning, "All is Grace - A Ragamuffin Memoir"