Christians - how can you have it both ways?

I'm only posting this to my Christian groups and, obviously, my friends list. If you're not a Christian, please don't bash Christians or make rude comments. This post is intended FOR Christians to respond.

I'm watching news and they are showing part of a debate among 4 people plus the mediator regarding "Is Satan Real?" 

I find it rather odd... at least one of these men who say Satan is not real is a former "demon caster-outer" for lack of a better word. But he now claims that Satan is not real.  I realize MANY people don't believe in God, Jesus, or Satan. But how do you claim to believe in God or Jesus and not believe that Satan is real?

Satan was created as an angel, the angel of worship. But, God gave angels (and man) free will. Satan tried to usurp God's authority and was cast out of heaven and, to this day, has "reign" over the earth.  At least that's my belief based on what I've read in the Bible.

I found the debate interesting, but I just don't understand how you can exclude Satan from Christian beliefs. I also don't go around blaming Satan for every wrong thing in my life. He doesn't have that much power or authority in my life as my life belongs to Christ!  But, I do believe he wreaks havoc whenever & wherever he can.