Joining a monetary union will mean giving up your national currency and adopting a new currency or a currency of a larger country. To some people giving up your currency is a provocative notion that could be equated to treason. This is especially true for small, developing countries that might have just gained their political independence.
The idea of being subsumed by a larger country is not appealing at all. Why, then, should a country want to enter into a monetary union? The increased interest in monetary integration is closely linked to the process of globalization, especially financial globalization, which has been a dominant feature of discussions at various forums.