Not surprisingly, Klingon cosplayers seem to attract a large number of military types, police officers and others who are drawn to those qualities embodied in the Klingon characters. As Anijar notes, these are not your typical Trekkies. In fact, they consider them “bad asses of nerdom" who like to work out and indulge in swordplay with Klingon-style weapons. As the author says, perhaps it is better to play Klingons than join a private militia, but there is still an uncomfortable side to this fandom.
The “smoking mirror” concept (Anijar, 2003, p. 136) posits the theory that such role play can aestheticize violence and barbarism without seeing ourselves reflected in the play. The Klingons cosplayers in this case adhere to a code that would unacceptable in normal society because it glorifies a Viking warrior-style creed of murder and pillaging in the name of the homeland. Other races are seen as less worthy and deserving of conquering, much in the same way that colonizing forces throughout history sought to dehumanize and reduce those they encountered to lesser beings or even property to be bought and sold.
There is also a racial element at play in the Klingon cosplay where mainly white players apply a blackface of sorts to become more Klingon like. And of course the Klingon nature is closer to that of what white Europeans settlers would have called savagery. Interestingly, the earliest appearances of Klingon characters had a more white or tan complexion before growing darker with the evolution of the franchise. That begs the question of whether Klingon cosplay is offensive in the same way the blackface costumes are.
For some people, Klingon cosplay is similar to the cosplay of Drow, a dark-skinned sub-race of evil elves from the popular Dungeons and Dragons game. Here is one person's interesting take on both and whether they are racist in their view.
http://blackroleplayersorganization.blogspot.ca/2014/08/cosplaying-drow.html