When a person decides to learn French, for example, he or she is not merely absorbing the linguistics of the language, but everything to do with French and France. What he or she is taking in includes all the preconceptions about the French language, that it is beautiful, that it is romantic, that it is spoken along the Seine, and so on. I may be accused of stereotyping here, and perhaps I am, but this does not discount my underlying point, which is that most, if not all, languages come with some cultural associations attached. To speak a language well, one has to be able to think in that language, and thought is extremely powerful. That is the power and the essence of a language.
Language is culture.
Language is the soul of the country and people who speak it. Language itself is already culture, and therefore it is something of a moot point to talk about the inclusion or exclusion of culture in a foreign language curriculum. A counterargument could well be that some people who decide to learn French, for instance, have no inkling at all of French culture. Indeed, they may not even know where France is on the map. To such a counterargument, I would say that while there may in theory be cases of such isolated individuals, I believe that in reality this is rather unlikely.