Colonialism has always been driven by liberal politics ever since the enlightenment. Their excuses and propaganda are long since ready-made. They have to save people from their governments or backwards culture by force. How can you stand by? Do you care about all humans or are you a racist?

Colonialism was never sold to the masses in Europe as a money making exercise. Rather people were told they had to invade Africa to save the poor innocent Africans from the evil Boer or the evil Zulu or some other evil group. They had to go into India to save people from their evil women killing religion or the evil caste system. And they didn't have to make anything up, all this nasty stuff was really happening which made it very hard to argue against intervention. But of course you don't have to send the army in to solve these problems, often it makes things worse.