There are like 60 countries to choose from which already have islam as state religion.
Because they suck? What happens when muslims become a large majority is that islam drives out any other competing form of ethics or morality. So debates over morality (a sign of a healthy society) are replaced with conformity to a particularly backwards form of religion.
The suppression of competing forms of morality is followed by intellectual stagnation since science is not allowed to make any claims that conflict with the holy text.
Poland is mostly Roman Catholic but public debates on what is and what is moral are not restricted to church doctrine.
Colonialism is a distraction. Yes colonialism harmed many countries but places mostly became colonies because they were poorly organized in the first place.