The colonial/imperial justification is usually that the 'natives'/'savages' were not exploiting the land to the fullest extent (usually based on agriculture); often calling it 'waste land'.

Therefore, by not exploiting it (enough, or the 'right' way), it 'naturally' belongs to someone (else) who can/will exploit it.

Not getting a response is like due to them not even knowing that much history. That, or you just broke their cognitive dissonance, at least until they changed the subject.