Sorry, slow zombies are for old people. Fast zombies are where it's at. Why? Because they're fast. You can escape slow zombies, but imagine trying to outrun a zombie that can run a 4.40 in the 40-yard dash. Slow zombies are silly in comparison.
"They're so slow. We could just walk right past them. I wouldn't even have to run."
Plus, the velocity of how the disease travels with fast zombies is just far more terrifying. Imagine going to bed, then waking up to a post-apocalyptic zombie nightmare. That's way scarier than the slow burn of plodding zombies.
Fast zombies are all style, no substance. There's no menace. The real cruelty of slow zombies is the false sense of hope they inspire, because people believe they're so avoidable and that leads folks to make fatal mistakes. To be slowly torn apart due to your own stupidity, thanks to overwhelming numbers and hubris, is a fate worse than a quick death.
With slower zombies, however, escape, perhaps even triumph, is theoretically possible. The danger they represent is less an overwhelming one and more an omnipresent one, one that can strike when you, for even a moment, turn your back on it.