I see mostly advantages of teaching any foreign language in any country. Just as students in the United States have an advantage if they leave school bilingual, so will students in other countries, especially if the language they have learned like English, is widely used across the globe. Speaking English as a second language gives you an advantage in travel as well as business, particularly in our current global economy. English is not only spoken in many countries but can often be the common language amongst people who speak different languages. Academically the ability to read in English, opens up an enormous amount of opportunities. Reading something in its original language is always to the readers advantage; "lost in translation" is not just a clique, it is an actual truth.
On the other hand English is difficult to learn as a second language because it does not follow grammatical rules as easily as other languages, particularly the romance languages. In additional English has many forms (British English and American English just to start), many dialects, many regional words and phrases, as well as an abundance of idioms and colloquial language used even in formal settings. Lastly there is some stigma to teaching English in areas where America in particular is the prime enemy. Teaching English may be thought of as Westernizing in areas that do not want or need to be westernized.