A lack of demographic diversity is only an indicator of a lack of meritocracy if you believe that bias is responsible for the lack of diversity.
For you, diversity might be important, but for your trash-talking colleagues it's probably irrelevant. (Even if you buy that a lack of meritocracy is generally demoralizing, which I think is a pretty weak claim.)
Clearly it's not important for those colleagues. I'm honestly curious as to why, given that I believe that the behavior in question seems to me anti-meritocratic (because it drives away worthy people from wanting to work with your team).
I also don't think "trash-talking" is really the right phrase, as it connotes a kind of equal back-and-forth among peers. That's not the behavior I observe; usually it's pretty one-sided.
For you, diversity might be important, but for your trash-talking colleagues it's probably irrelevant. (Even if you buy that a lack of meritocracy is generally demoralizing, which I think is a pretty weak claim.)