Being a bilingual has a great quantity of huge advantages...you may travel to different countries and communicate yourself with people who don't speak your language feacally, you will find a job easily among others.
The disadventages are minor but there are some, for example, you could make a mistake when you are speaking, you could mix words of a language without realizing.
In my opinion, everyone would have to be a bilingual, so everything would be easier and we could communicate each other with any problem, we could live or work in differents countries withou the impediment of not knowing the language.
So, being a bilingual would open us many doors to progress in our life and keeping forward. Countries would have the opportunity to advance with their development and the unemployment would fall.