An explosive spur of the moment dust-up between two middleweights isn't the kind of bout that invokes such thoughts. It's usually a pair of long-standing heavyweight goons who casually challenge each other while a faceoff is taking place and then doff their gloves and start throwing after the play begins.
A bit strange and no surprise it causes some hockey watching newbies to scratch their heads and wonder if this part of the game is on par with "professional" wrestling.
Another aspect of fighting that brings into question the mentality of the players involved, is when one or both are wearing visors while throwing punches.
This doesn't seem to be a habit practiced by only those individuals who rarely ever get engaged in a fight (see Sidney Crosby's recent scrap.) For someone like that it would be completely understandable. In the heat of the moment and focused on protecting yourself and flailing wildly, removing your helmet is the last thing to be considered.

The number of critical comments may also be due to his high-profile and the fact that he causes a lot of damage to other teams with his scoring and hence is singled out for those times when he keeps his helmet and visor on when fighting.
There is actually a penalty in the NHL rule book that addresses fighting with a visor:
Rule 47.6 states:
Face Protection - If a player penalized as an instigator of an altercation is wearing a face shield (including a goalkeeper), he shall be assessed an additional unsportsmanlike conduct penalty. Should the player (including a goalkeeper) who instigates the fight be wearing a face shield, but removes it before instigating the altercation, the additional unsportsmanlike conduct penalty shall not apply.
I can't recall this penalty ever being called. It is contingent on a player being tagged with the instigator penalty first. With the fighting major and unsportsmanlike tacked on that would add up to nine minutes. Something that is rarely seen on a scoring summary. But the scenario that is given as an example in the penalty description rarely occurs because those players who wear visors are least likely to initiate such a confrontation.

It seems as if the laying down of helmets before a fight is more ritualized in the junior ranks where pressure may be greater to adhere to some fighting "rules." Also, in many of those leagues facial protection is mandated and so the situation is the same for everyone.
For the longest time in the NHL players did not wear visors and so it was not an issue. There was no need to remove helmets before a fight though misplaced punches still resulted in many a dislocated knuckle or broken finger.
As more and more players have started wearing visors and fighting has remained a condoned and accepted part of the game, it hasn't really been addressed too much beyond the obscure rule mentioned above.
Perhaps it's being left to the players in the hopes that simple common sense goes some way to reducing the number of slug-fests. Two players with shields who decide to battle and keep their lids on have to live with whatever hand injuries come their way. A player without a visor who goes after one with, is simply accepting the inherent disadvantage.
Regardless of whatever sense of honour there is in making it a fair fight, even if there is enough time to remove a helmet, there is something in-built that results in an aversion to exposing yourself to further danger. But a player with a visor who initiates or even mutually accepts an overture to start throwing haymakers, should have some obligation to remove his extra protection or face an additional penalty.
Unfortunately for those players who like the intimidation that the potential for some fisticuffs provides, they may have to accept that visored players enjoy some added insulation. Their decision to wear the shield increases the chances of hand injuries for opponents and reduces the likelihood that they will end up in a fight.
In fact, visors can and do also result in some face injuries for players who keep them on during punch-ups. But it's common sense that a player is better off with more protection when staring down a possible on-ice hammering and will probably avoid the kind of nasty season ending injury recently suffered by Mark Bell.