system
Given the following post, respond as if you're commenting on Reddit:
human
[The Walking Dead] How did so many people get infected with a virus that, ultimately, is slow moving and ineffective?

There are hordes of zombies in the walking dead- invariably, there is a cloud of zombies out and about. Where do they all come from if the only realistic way to make more of them is for someone to get bitten and then escape until they can turn, barring aside the odd starvation or shooting. The zombie virus isn't very effective at spreading, in and of itself, as the zombies will eat the corpse given the opportunity, leaving only a gasping head.

All in all, I would choose a couple police officers aiming for the head over a small hoarse of zombies any day. Why was society so quick to fall against such an ultimately slow moving disease?
gpt
Confusion, emotion, panic travel, and some airborne vector. 

The virus itself seems to be airborne, but not lethal. Its like a passive disease, sitting dormant until you die (possibly from a zombie bite, but doesn't need to be).   So, in that way, the virus spreads airborne quickly, worldwide.

The visible symptom of the disease are the zombies, of course.  These do not need to spread from a single source, since death from any cause creates them. 

The zombies in one area would be devastating initially.  Residents would report 'home invasions', and be killed.  Police and other first responders would be confused and also turned into zombies.  Military bases would deploy, but without training or protocols.  Many military might get bitten, return to base, and cause chaos there.  Others in the military might go AWOL to protect their families near the base.  This would happen simultaneously in many areas.  

People would begin to hear news reports, and would be confused.  It does not even take a panic - even calm reasoned action would just add to the chaos.  Massive traffic jams would lock people in the cities.  In the country, people live in homes with lots of windows, etc.   

A few people who survive the zombies then are unaware that any death brings more zombies inside your walls.  Bitten survivors turn, or people die from infighting or just from the risks of living on the run.  Even the moment of contact with such zombies would be emotionally shocking - seeing your resurrected but insane child or other loved one - and thus people would die that way.  

What remained of the military might try to set up safe zones, but beyond safety, there would be food distribution and other issues, and eventually they might just pull out to look to saving themselves. Even that might not work, since there is no real safety where any death leads to zombies.

In the end, its not until there are aware survivors, living in secure areas, that the plague might be stopped.  Places like historic forts, islands, moutain areas, walled prisons, walled military facilities, or other areas that could be protected easily would become bastions of survivors. 

What should happen though is a massive decline in the number of wild zombies at some point thereafter.   While we do see some decay, it appears that even after years, most of the initial zombies still seem to be actively walking.