I think its excusable, due to the fact that every Star Trek series has been about humans, not Klingons. This is the reason I get so annoyed when people say the next series should be on a Klingon ship or something.
When youre writing a show which aims to take a closer look at humanity, its useful to have something to compare humanity to. This is the basic staple of science-fiction, taking humans, and judging them against something else. If you look at the time when science fiction began evolve, people were very much looking away from humans as unique and unfallible. I dont think its a coincidence that a move away from traditional religion, and towards humanism, is happening at the same time science fiction is getting popular.
So, if you want to examine humans by comparison, it makes sense that the comparison species you use be fairly unrealistic, and this applies to nearly all the races we meet in Star Trek. Ferengi, Klingon, Vulcan even Data. None made sense in any way, but that was good, because using such broad and unrealistic characters allows for a more interesting and dramatic reaction. Ferengi are ridiculous, no society could ever evolve like that, but its because they are so specifically created that we get those great moments of comparison, like when Quark berates Sisko for looking down on them in 'The Jem'hadar'.
I think this is just how drama works. Sure, the Klingon's arent realistic, but thats what makes them interesting in a show like Star Trek.