If you're referring to the Koon-ut-kal-if-fee, it was an ancient marriage ritual that usually didn't involve a duel to the death. The kal-if-fee was also something not known to many non-Vulcans.
My point is that even after it was known of, the Federation didn't put an end to it,
Would they even have to? See below.
Because the ceromoniy was the Vulcan heart and soul. It was intergral to who the Vulcan are.
Only in the sense that it shows the Vulcans at their most savage and emotionally vulnerable, but otherwise it's in contradiction to the Ways of Surak and the path their society has taken since the Time of Awakening.
As far as the ceremony, though, that's
kah-if-farr--the actual wedding. Kal-if-fee--the wedding challenge--was something T'Pring invoked from ancient times and would seem to be in direct conflict with both Federation
and post-Surak Vulcan society. T'Pau allowed it, but another Vulcan officiating the wedding may not have.
And for all we know, that was the first kal-if-fee since the Federation was formed--and nobody actually died. The next kal-if-fee we saw was more than a century later aboard the
Voyager--and nobody died there either. As T'Pau has been proven wrong at least twice, I would argue that kal-if-fee doesn't
always mean somebody dies.
The federation adapted to the fact that some of it's members fight death duels over women. "They" didn't throw the Vulcans out.
And they may not ever need to if nobody actually dies during those death duels anymore or do so
very rarely. More people may die from rock climbing on numereous Federation worlds.
And the Klingons, with all their bag full of "querky" customs would enjoy the same ackowledgement of their diverse ways.
Only to a point, IMO. As I said in an earlier post, I don't think Federation society is an "anything goes" society. While I do think each individual member world maintains its own local laws and traditions, I think each member world has to have more things in common than different with the Federation to become a member. I think the only way the Klingons could become full-fledged members of the Federation is if the Klingon Empire as we know it ceases to exist--either figuratively or literally.
Look at it this way, if say the Trill (name out of a hat) didn't agree with the concept of arranged marriages, they through the federation couldn't say boo to the Vulcan and Betazed practice. If the Betazeds (who do have arranged marriages) didn't like death duels, would have no say in Vulcans dueling. If still another federation member practiced genetic engineering, Humans with their ban on the practice couldn't make them stop.
Not acceptance, just simply tolerance.
I think there are
some things the Federation
won't tolerate among its members. I also think that those worlds that may find Federation laws too restricting are free to say "I like you, I'll work with you, but I don't want to
be you." That's tolerance of another kind.