To some groups, the word Allah merely means God in Arabic and there is nothing special about the word and there should not be a big deal about using the word. However to some groups, the word Allah is more than the Arabic word for God. The word Allah is a name that is holy and sacred and there is a strong emotional attachment to the word Allah and hence should be exclusive.
Now to those groups who say that Allah merely means God in Arabic, why has the Arabic word been chosen for the Bahasa Malaysia translation when there is a word Tuhan for God in Bahasa Malaysia.