I lived in the Collier Hills area for 6 years and violent crime never impacted my life. Having only ever ridden the Red/Gold lines of MARTA and mostly during day, I only ever felt unsafe when people with obvious mental issues were yelling on the train - although I never saw violence. Parts of Atlanta are perfectly safe, and parts of Atlanta are a sad depressed economic wasteland.

I love Atlanta, but let's be real: the northwest side of town is getting better but it is hardly "perfectly safe". People have been held up at gunpoint on 10th Street where I walked daily, literally across the road from Georgia Tech, in the middle of the day. My old house in Home Park -- about a mile from Collier Hills? -- was broken into in broad daylight. A house three lots down the street was raided by police because some criminal organization was being run out of it. At an apartment complex I lived at in the same area (10th and Northside), the apartment next door to me and a bunch of others were broken into. In the parking garage at that same apartment complex, a Georgia Tech student was shot in the chest during a random crime and very nearly killed. These are just the incidences that I remember and that I have a fairly close connection to, as a counter to your own, more fortunate anecdote.

Echoing Kelsey's sentiment, I also grew up in Atlanta, lived in Home Park, and while I wouldn't say that I felt unsafe while I lived there, I now live in an actually safe place. It's unbelievably different. People actual walk around. I see women walking alone. I don't see sketchy people, I don't have to lock my doors (my house in Home Park actually had two deadbolted doors before you could get inside). The red line prior to five points is well known to be the safest line, but people still harass you on it. I don't know when you lived in Atlanta, and I was only taking Marta the last three or four years that I lived there, but it's definitely not good/safe public transit.