Are their bad parts of Denver though? Other than some of the alleys downtown.
Each city has good areas and bad areas, I remember I ate at a restaurant in LoDo - which was transformed from the bad part to one of the nicest now - and that night there was a shooting at like 3am. I think time is probably biggest central factor to crime, areas that normally fine in daylight become iffy when the sun goes down. East Colfax is probably one of the bigger ones which changes to an iffy state closer to night time, but it's absolutely fine during the day.
The borders of northeast Aurora and Commerce City is probably one place I wouldn't ever go to; plus it's just an ugly part of town and has absolutely nothing to do there (big manufacturing part of the city). Actually, the parks right in front of the Capitol have been increasing in shadiness (not sure I would go there at night either). Colorado Springs is sort of iffy to me too, but I think that's because of the military bringing in all these people across America to a focus point city. I've met a lot of cool blokes by playing hockey in those areas in the past, but met a lot of weirdos too. Oh and Colorado is unique because there is still a large percentage of weird mountain men hermits too, not as much of the States up North, but if you go into one of the smaller mountain towns I guarantee you'll find someone. With that said, I am pretty sure that some cities have it worst than the ones you find in CO.