It wasn't at all hard to see why they were dangerous. They were mad. The virus within them made them see things. They were dead set on destroying anything that moved, all in the name of keeping themselves alive. They weren't human. They were monsters. What really set them apart from other people, though, were their bloodshot eyes.
That's why I've barricaded myself indoors, forced to resort to my own pets as food... I feel horrible, but that's what it takes to stay alive in this apocalyptic world. I hear them banging on my front and back doors, see them staring through the window growling and sputtering. They've had me surrounded for days.
I found a dusty old mirror in my room just now. I take a look at myself for the first time in weeks, and I see a red haze filling my eyes.