The U.S. has been called the Great Melting Pot because so many cultures had combined to create a somewhat unique culture, a.K.A. American culture. Some other have called it a salad bowl because even though even though many cultures are mixed, they tend to hang onto their own culture. In my opinion, American culture tends to be more of a stew pot where parts of each culture are mixed together yet still have chunks that have changed little if any.
Combining cultures tends to work fairly well as each culture tends to have a positive effect on the others but this is only good to a point. We all know that some cultures have some less than American ideals, for instance, some cultures still tend to teat women more as property instead of as equals to men. If they immigrate here and mutually agree to their native culture, then that is okay unless it effects our existing culture in a negative way, such as passing laws about women that they may have in their old country. Obviously any illegal practices should not be allowed much-less be allowed to influence our culture. Another factor is the extent of influence. Recently I have seen a trend in our shifting language. In the past, a new culture learned, for the lack of a better term, American English. Along the road, their own language is also represented in American English. In more recent times, one language, Spanish, has not melted in very well. Instead of the new immigrants having to learn English, it seams like there is more and more pressure on U.S. citizens to learn Spanish instead. Instead of commercial an public signs being in English only, more and more of the signs are bilingual. Though this may be okay if the town is near the border of that culture or if the town was founded by people of that culture, such as San Diego, but up here in the norther mid-west, if anything we should have signs in English and French because many town were founded by French speaking groups and that we are across the border from French Canada. Yet the only signs in french are the names of the towns themselves. Influence is one thing, take over is a different subject.
Frankly, it's strange that anyone would offer the question, although with the recent (and not so recent) world-wide disturbances, I suppose that it isn't all that odd that anyone would pose the question. However, whatever the situation, we must see that it is beneficial to society to have outside influences. One last thing before we get into the specifics: The topic doesn't ask us to evaluate in regards to a specific outside influence, so we will be regarding the influences as general, instead of simply China, Russia, North Korea, etc. All that being said, let's go ahead and move into our first point, which evaluates what happens without influence.
1) Isolationism is detrimental
For this point, let's take a look at North Korea. It is the closest to a totally isolated country we have in our world. It's society: pushed to the brink of survival every single day. The reason is quite simple: North Korea does not interact with the outside world, instead, it shuns all influences in order to create what it believes to be a perfect society centered around Kim Jung Un. Because it has taken this stance (or rather, been brainwashed into it), it has seen little to no progression. The same may be said for China before the Mao revolution (whether or not this was justified under Mao is another debate, here we simply see that the previous society was non-progressive). So, now that we've seen examples of isolationism, we see that a lack of influence is detrimental to progression. This is not the only reason however, so let's move on to our second point, discussing the "acceptability" of taking in other culture.
2) A Kaikin government infringes upon the rights of its citizens
John Locke spoke at great length of "Intellectual Property." Though he is long dead, the idea remains the same. The government has no right to tell citizens what it may or may not think, as this would be totalitarian. The same idea applies to the introduction of other cultures. So, we see that the restriction of intellectual property is not justifiable under, well, frankly any government.
In conclusion, we see that isolationism is harmful to any society, and that progress can only be achieved through cultural diffusion, rendering it ineffective, no matter the situation. Next, we see that any government the deems outside influence 'unacceptable' is not in it's countries best interests.
Pulling it all together, we find that, in general, it is almost always acceptable for a culture to welcome outside influences.
As we all know, outside influence changes how everything was for generations, and insert new ideas and ways for people to live their lives, and the result would be harmful, or even deadly. As we all know with the lionfish, they were invading many bodies of water and are harming the water ecosystem. So the question in mind is: is it worth it to take the risk and change things that we once do every day for generations, when we don;t even know what the outcome would be?