I will go with everyone else and say that people fear what they do not understand. It is odd though, as a lot of people in the furry community debate on what constitutes being a furry is. Is it when you like the idea and aesthetic of animal people? Is it when you find them sexually appealing? Is it when you prefer animal people characters to that of regular humans in media or real life? Quite the conundrum, but that is beside the point.
I think people see the bad or more extreme/odd side of the community and only focus on that. To some, furries are a bunch of gay men in animal themed costumes having orgies in the middle of a convention hall. I have no problem with "fur suiters"(people who wear full body anthro animal costumes that are furries), gay men, or orgies, and yet it is for some reason a negative image that some people think when you mention the word "furry".
I blame CSI and 4chan mostly for the negative image that furries get, as anyone who is knowledgeable about either CSI or 4chan would tell you that they do/did not represent furries very well(not to say that 4chan doesn't take the piss out of only furries, hell, nothing is sacred over there, and that works just fine. Even then though, 4chan or b in particular mellowed out the furry hate quite a lot).
As for anyone who is curious on what an average furry is, well I am an example. I figure most furries like myself just enjoy the aesthetic look of an "animal person". Many furries look at or make art, music, stories, and other forms of media that are anthro themed. Some of the media may be erotic, some not.
I mean not all "gamers" are 12 year old americans with a potty mouth, but that is what some people see us as. So why dont we all just get along and hold hands eh?
Edit: I also have to mention that people with persecution complexes tend to exist in all sorts of fandoms, but for some reason furries seem to be the well known for it. I suppose people should just chill and not take everything as an insult, or perhaps they should not "jump the gun" so to speak when it comes to debates about furries.