Why did the British kill the aboriginals?

There were a number of reasons why the white British settlers had conflict with the indigenous people of Australia. Primarily, it was the feeling of white supremacy, the sense that they were superior, and that the Aborigines were mere savages, not really even considered people. The British were out to conquer the land, regardless of anyone or anything that stood in their way.

There were many cultural misunderstandings: the Aborigines were naturally a generous and sharing group of people, and they had no concept of ownership. When they were trying to "share" the british stock animals, this was seen as theft and, in a struggling colony, was an offence punishable by death as far as the white settlers were concerned.

Some groups of british aimed to decimate the aborignal population entirely, thereby being able to gain the land for themselves. Naturally, Aborigines reacted with some hostility to being forced off their own land, but their spears were no match for British guns.