non-long-recognized-by-cultural-tradition context.
Worf said:Sir, I have acted within the boundaries of Klingon law and tradition.
But it is recognized as Klingon tradition and Picard says as much in Reunion.
Plus I'm confused why the Federation would deny rights to its' citizens that come from outside its' borders that it grants to those who are from Federation members?
From a Federation perspective, the fact that a Klingon vengeance battle is held in an uncontrolled fashion in which both parties do not have the option of backing out probably means that, again, from the Federation's POV, Worf violated Duras's rights. The Federation is willing to abide by the rights of its citizens, including the right to choose to engage in consensual homicide, but it probably argues that its citizens do not have the right to violate the rights of others, even if foreign states say they do.
In other words: The fact that the Federation is tolerant of, say, the Klingon vengeance battle tradition does not mean that the Federation views Klingons as having a right to do so. There's a difference between being tolerant -- which in this context, means not telling a sovereign foreign power how it ought to run its society -- and refusing to stand up for what you believe is right. Moral relativism within limits.
To make a comparison: Most Americans today would find the concept of female genital mutilation to be horrific and deeply immoral. But there are also many who do not think the United States has the right to tell sovereign foreign states what practices they may or may not allow. The U.S. does have a practice that may be argued to be similar in the form of circumcision -- but, there again, very few men who've been circumcised report any trauma from this. So we can draw a comparison there between two cultures that have related practices with key differences that cause one culture to view its practice as acceptable and the other culture's as unacceptable. The U.S. allows circumcision because it does not view it as causing trauma in those who are circumcised, but it abhors female genital mutilation because of the trauma it causes; the Federation allows ritualized homicide when it's done with mutual consent, but it abhors Klingon vengeance battles because they are not carried out with mutual consent but are forced upon one party by the other.
Seems to me the Federation is full of double standards when it comes to morality.
Seems to me that you're confusing tolerance with an absolute belief in moral relativism.