Demons are most definitely real. Anyone who thinks otherwise hasn't watched enough TV programs about it. There are numerous cases of families being tormented by demons. These are ordinary families who have no reason to make up such stories. How would that benefit them when people like the flying pig guy will mock them? It is usually discovered later that some kind of Satanic cult had been at work in that location previously. Sometimes they find the actual thing that was used as the portal between the demon world and the earth, like a well or some kind of pit. I saw one story where it was a well back in the woods behind the house. The guy went back there and the demon appeared and he got possessed by it and had to get it excorcised out. Another case involved a deep shaft that was found in the basement of a building and they found that satanists had been doing demon summoning rituals down there in the past.
If you don't believe demons exist, you're just very ill-informed or you don't have sufficiently good judgment to tell when the evidence is overwhelming. It is not at all difficult to summon demons using magical spells, and then it is very hard to get rid of them. Think about it, if demon summoning never worked why would there be books about how to do it and why would those beliefs have persisted over the centuries? Somebody would have noticed that it never actually worked and people would stop even attempting it.
Look at this forum post I just found;

"This is my first time posting but a couple of years ago i bought a new house. It had heavy "malevolent" manifestation problems. We found the problem... a portal in the basement and sealed it. All ended until recently. A black mist now seeps around my basement and the portal is open. I fear that i can not protect my family. Please someone help me close this portal." http://www.mysticalwonders.org/group/about1685.html

What about THAT?