To me it's pretty obvious not all cultures are good to mix with.
Which isn’t terribly far fetched - apparently some gladiators were basically sports stars, with death.
The answer to bad ideas is not to isolate them. It's to outcompete them. The battlefield of the modern world is the hearts and minds of it's citizens. If our morality is superior and our ideas are successful, we should just keep doing what we do and let them spread, like a virus.
This reads a lot like "everything is a social construct".
A culture is a property that's shared by the population. The absence of such a shared property is not its presence.
New is good, anything else is death. Anyone pining for a 'good ol days' culture is chasing a mirage that never existed in the first place and will do damage to themselves and everyone around them by trying.
Are you making the analogy because it sounds poetic, or because it actually makes sense? Humans are not plants, and they're not grown or raised to be killed for someone else's benefit.
If you insist on the analogy anyway: livestock are homogeneous just fine. Also you seem to be forgetting that weeds and invasive species are also things that can destroy ecosystems.
> New is good, anything else is death. Anyone pining for a 'good ol days' culture is chasing a mirage
That's what a melting pot is. It creates something new. You seem to be struggling to understand what people are actually arguing for or against.
Have some sense of perspective and you'll be less likely to turn into an old bitter man, shaking his fist at clouds.