1. M-16's are not semi-automatic. They are select fire. AR-15's are semi-automatic.
2. The .223/5.56 cartridge is not "high-powered". It is an intermediate cartridge, at best.
3. Apparently neither the mayor nor the author of the article know shit from wild honey about ballistics. Soft point .223 is actually safer in an urban environment than heavier handgun rounds. Due to their velocity and light weight (55-62 grains vs. 230 grains in my personal duty pistol), they fragment upon impact with walls, reducing risk to bystanders. I really wish politicians and the media would educate themselves before shouting the anti-gun meme like braying jackasses.
Hit the link and read the comments. The Mayor gets himself well-flamed.