Man that first post, are we sure that's not a spam bot? lol
Justification and/or fanboy blind devotion. The M4 certainly has them like few other firearms. (the only other gun that comes close in my mind is everyone's recent love affair with the "Staccato". STI made these 2011 pistols for years and they were scorned by "real shooters" as gamer guns and not to be taken seriously. They changed the name of the company, made them black, hung a bunch of shit all over them and now they're every Timmie's ultimate wet dream pistol.)
"When going down this rabbit hole the one shotgun that kept coming up over and over was the Benelli M4. Everything about it shows it as being the most effective tool for the job." What job is that? That's the problem. It's a job that almost no one who buys them is actually doing. (and I don't mean pretend practicing to do it, "training"., LARP'ing and fantasy camp with guns.)
The M4's problem is it's one trick pony. That problem's not exclusive to the M4, other than that it's only available in the one dress. (short barrel and ghost rings) Plenty of other guns come like that, but unlike the M4 they also come in other variations.
The "issue" comes when people buy what they really don't need. Don't take that the wrong way, people can buy whatever they what for whatever reason the want, or no reason at all. Lord knows I have dozens of guns I sure don't "need" or use for their intended purpose) Like anything else when you try to press it into service for other tasks, yes you can make it work to some degree, but it will never work as well as the right tool. And that's what people are pointing out.
The M4's "problem" is too many people buy it because they saw it in movies and video games and know it's the bestest gun ever. (It very well may be, but if it is, it's for doing things they don't do)
The old saying was "Beware of the man with only one gun, he probably knows how to use it." Years ago when I worked at a large public shooting range, my mind was changed to "Beware of the man with one gun, he probably hasn't used it in a really long time." Now it might be, "Beware of the man with only one gun, he bought it because of a video game."
Anyway... back around the the very first thing I wrote before adding all of the rambling nonsense above: I suppose it's all about realities. For ME, I've yet to come up with anything my M4 does better than the other models. That's ME.
(other than yes it kicks a little less than my inertia guns, because it's gas and almost 2 lbs heavier than a similarly appointed M2. But that is of minor importance to me.)