However if one fully applies the metaphor there is also an implied correct behaviour towards the "zombie" - put them down using lethal force.
I agree with Denis on this point. You often see this type of zombie post on gun forums where you wonder if the poster is even old enough to own a gun, or else they are too immature or crazy to appreciate what those weapons are really meant to do, i.e. cause severe bodily harm, even death, to another human being. These are the kinds of zombie posts that I have tended to run across in my own web surfing, which is why I'm not a fan of zombie-themed posts on ETS.
There was a question asked on ETS just recently about the effects of shooting into a crowd of people--"legal issues aside". On some abstract level, I suppose it's a legitimate question, but on a gut level, throwing that question out on a public forum like that made me cringe. However, if the question had been couched in terms of shooting zombies, well, ha-ha, that's different, so yeah, let's talk about the most potent ammo to use, the best ways to put them down, etc.
The zombie metaphor has become an excuse to talk about subjects like that without necessarily appearing like some psychopathic mass murderer and to conveniently ignore the reality of what the aftermath of those actions will be. To take glee in such topics amongst strangers doesn't seem healthy nor desirable to me.