Why would you have to be able to enjoy another culture? As long as the cultures live apart and don't bother each other, it's good enough.
Just like being vegan. As long as I don't force you to eat meat and you let me enjoy a stake with cheese, all is good. But once we try to establish baseline (either all-vegan or mandatory-meat), all goes down the shitter...
Multiple cultures are not like multiple dishes for a meal.
There are important and often deadly conflicts (e.g. coercion, mutilation, poverty, war) related to cultural differences and (IMO bad) cultures themselves.
I am in favor of a prohibition of cheap animal products because of the economic, ethical, ecological and medical problems related to animal products.
I am in favor of a limitation or prohibition of certain cultures. E.g. the Islamic veil or family customs that lead to psychological and physical harm or forced marriages.
My point is that looking for common baseline for everybody even for a meal leads to conflicts. While coexisting at peaceful terms is less conflicts.
On top of that, even if we'd come up with a common baseline, I'm sure people would invent differences in no time. Give it some time and somebody in vegan culture may realise that animals are edible and damn tasty.
Prohibition of cheap, all-shortcuts-taken, foods is not vegan issue. Veggies, animal-related foods and meat should be responsibly made and focus on quality (as in nutrition and taste, not only nice looking) rather than price alone.
You'd have to redo Islamic culture from the ground up and forcefully reeducate several generations of people. And it's questionable wether it'd be a success. Soviets and Nazis did try to build the new perfect man. Neither approach was pretty. Let's not go down that path again. Yes, some people may seem backwards (as we do for them). But hey, live and let them live. As long as neither of us bother each other and live in their own countries ruled as each of us see fit.
Unfortunately not even European countries respect the human rights with regard to poverty (economic, social and cultural rights) and freedom of expression (civil and political rights) and international law regarding warfare (e.g. Libya, Yugoslavia,...):
And even Human Rights (tm) is interpreted differently :) Especially given how much of a failure UN is.
Also, world-government formation would be a blood shed not seen before. On top of that, all similar formations so far couldn't hold their shit together. USSR, British empire, Roman empire.. EU is struggling too. Even China has tumultuous history and they'd have issues the moment iron grip is loosened. USA is not exactly without internal rivalries either.
Why go through hassle of forming such entity if it will fail sooner or later?
Just like being vegan. As long as I don't force you to eat meat and you let me enjoy a stake with cheese, all is good. But once we try to establish baseline (either all-vegan or mandatory-meat), all goes down the shitter...