Boy, I bet the guys who did Zombieland feel stupid about not having any zombies in their movie.
Fuck those clowns!
Zombies are slow shambling, and easily defeated except in a group. Rage infected people are fast, mindlessly violent, and just as dangerous singly. That make28 Days Later more a “soccer hooligan” movie. 
For me, zombies have one defining feature. Unstoppability. They can be fast, they can be slow. Doesn’t matter. They can be downed with a shot to the head or a shotgun to the chest. Doesn’t matter. You can kill one or you can kill a million. Doesn’t matter.
They keep on coming.
They’re zombies because they’re magic. As much as they tried to make them non-magical-zombies by making then not-undead and caused by a real virus; the magic comes in when they work together to attack the non-infected.
Could a virus make humans blindly aggressive and voracious of anything it attacks? Sure. We’ll call it the Bath Salt Virus. Humans have an aggressive predator genetic instinct. I’m willing to believe it can be turned on by an infectious virus. But, such humans, acting on ramped-up instinct should attack any animal and other infected humans.
No virus could mutate so quickly to give a human a human-only-but-not-other-infected-human bloodlust. Therefore, magic! And therefore, zombies.
I would note that you’ve just additionally disqualified Planet Terror, Cell, I Am Legend and its film adaptations, and at least one of the Return of the Living Dead movies from the zombie genre.
Ack, the hamsters ate my post…
To me the fundamental aspect of zombies is they’re former humans now out to get you, and when they get you, your body becomes one of them. Not undead, not slow moving or unstoppable, or any of that. The characters are often fighting and running from people they recognise, and the fear of not just death, but worse: eternal mindless servitude to the enemy.
Thus the infected of 28 Days Later are zombies. So, too are the pod people of Invasion of the Body Snatchers and the Borg of Star Trek TNG. Vampire stories where you become one upon attack would also qualify if that fear is emphasized.
I can’t believe people are still arguing about this.
These zombie chauvinists would have their heads explode seeing video game zombies where they operate chainsaws or have rocket launchers for arms. 28 Days Later is downright pedestrian.
No reason why this hypothetical virus couldn’t key on some kind of chemical marker and cause the infected to produce it. Same way lots of animals keep from killing their own tribe.
The magic part is that it takes seconds to go from normal to killing machine. Biochemistry just isn’t that fast. The very fastest infections take at least several hours for symptoms to show.
Why do you need to drag Resident Evil into this?
Are those zombies? They started out as standard undead, but you also have these bizarre mutated monstrosities, some with giant axes or Gatling guns grafted to their arms and whatnot.
The showrunner of Walking Dead once said that they exist in an alternate universe almost exactly like our own, the main difference being that neither the word or the pop-culture context of zombie have ever been created.