Of the hundreds of strains, only a few harm us, and really it isn't their fault. They are just sitting in our intestines, going about their business the same as all the other E. coli only they produce a toxin. Even then, most of the toxin produced isn't deadly. There might be some cramping, some nasty diarrhea, but nothing a little over the counter medicine and a couple of days won't cure.
But then there is E. coli O157:H7. It can cause the colon to bleed and the kidneys to fail, though honestly it isn't pernicious at all. Most people infected will just suffer the usual E. coli symptoms. Some will see a little blood. Only five or ten out of a hundred will seriously suffer and only one will be likely to die. It doesn't deserve its nasty reputation in news reports. Besides, it is our own fault there are outbreaks. It spreads through our own making from our factory farms and centralized food production.
Mostly E. coli lives a quiet life in our guts, happily helping us, content to live out their lives without our ever noticing them until they die or are flushed down our toilets. It is a friendly little thing. The bacteria most microbiology students culture first. It grows well, fast, easily, and only wants a little food once in awhile. The bacterial version of the houseplant you can't kill. It's round colonies rice up from the agar plates like smelly smiley faces.