One reason is the people who you're likely to run into on internet forums aren't the ones who live in the high crime areas.
Another reason is many people who say they're from Chicago aren't really residents of Chicago but the Chicagoland area. They live in the suburbs and either commute into work or come into the city on the weekend and spend their leisure time in the Loop area, the part of the city where tourists visit, the downtown area. Many people, people here in IL even think that that downtown area is the city of Chicago. Not knowing that the city itself is about 28 miles long going north and south and about 5-7 miles wide.
Every time I tell people I'm from Chicago they say, "Oh yeah? What suburb?" One time, I was in Oregon and I had to show the guy my actual Driver's License showing I had a Chicago address because he wasn't buying that I lived there. LOL
A couple weeks ago I was introduced to a couple who asked me this very question, repeatedly explaining, only to have them finally assure ME that I lived where I had told them I live. "Oh yeah, you guys are in the city" ??? I mean WTF? LOL
A lot of imports who came from the surrounding states, Ohio, Michigan, Wisconsin, Iowa, Indiana who came here for jobs, for a change from Pu'Dunk. Revel in the city's history, it's culture, it's mystique... It's a badge of pride to say you live in Chicago. You see the change in a person's demeanor, the awe when you tell them you're from Chicago. I don't understand it, but I find it amusing. It's like either your a bad ass, a Bad Bad Leroy Brown, or they think you're super wealthy living the highlife... It inspires the imagination I suppose...
As for the crime, well, you get desensitized to it. I live in a pretty affluent area, lots of politicians, city and state, high ranking city officials, lots of police presence and in the 5 years here, we've had car break ins, burglaries, weirdos and what not, but all in all it's a good neighborhood. You just "know". No matter how safe it seems, this is the city.
I myself love Chicago. Always will. Do I appreciate it now as much as I did when I moved here from the South Subs 12+ years ago? No. I'm older now and I don't need to be "on the scene" like I use to, but I will defend this city and all that it is until the day I die. Why? Because it's my city.
You have to live here I suppose to "get it".