I believe Kahoku is right, good lucky trying to change a Demon against its will, but Demons can and do whatever they please when they want to.
Now as far as Demons getting a bad wrap... When you watch the news and see terrorists, what do you see mostly? You might see the stereotypical Arabic male with an evil face doing dastardly deeds like eating babies or something miserable. You then might (if you have no other knowledge) think that these Muslims are all monsters, the news does not seek out and find those making a good example of themselves, it doesn't sell papers.
What concerned people in the past about Demons, especially in a Judeo-Christian world. If a Demon did something bad just to mess with them, or to consume energy from the fear... everyone knew about it, the news spread like wildfire. If a Demon did something to help out, protect, nurture... they just assumed it was an Angel.
Demons also get the bad rep from being associated with Chaos. Not that Chaos is bad, but it throws off our balance by it's nature. Demons thrive on making something happen out of the ordinary, whether it is good or bad depends on the Demon. Protecting someone if stopping someone else from utilizing their free will to harm them, thus it is doing some unbalancing. Freaking someone out is again unbalancing a life by scaring the daylights out of them, people don't like it.
think of a Demon as either the bully who just seeks to mess up your day, or conversely as the kid who sort of breaks the rules to help you out. The bully might pour out your milk, hang you up by your undergarments or pelt you with snowballs. The benevolent rule breaker might know you are having trouble on the test and move his sheet over to where you can see his answers, or possibly slip you an extra cookie at lunch (though if it were Kahoku I couldn't ever see that happening) or sneaking you out of your house to go play stickball even though your mom grounded you.
Both are chaotic, both are perceived very differently.
The maximum effective range of an excuse is zero meters.