This is different from, say, a wholesale sales tax, which taxes the transaction from wholesaler to retailer. GST taxes the transaction in which the household purchases a good or service.

GST is a more efficient tax than a wholesale sales tax because it reduces economic distortion. Suppose an arbitrary decision were made to only tax products which began with letters from A-M, and not to tax those which began with N-Z. Suddenly many more people would be producing N-Z goods instead of A-M goods, the economy would shift towards a A-M economy.

This not to say that GST is a good tax - it is just that it can be taken more efficiently from the population.

Given that the government takes money from individuals without their consent, it is in their interests for it to be taken as efficiently as possible. Given the choice of

1. someone smashing your car window and stealing your mobile phone; and
2. someone picking your car lock and stealing your mobile phone,

The GST is a way to take wealth from the population by causing slightly less damage than its alternative. It's not a good tax, it's just the lesser of the evils.

One of the main objections to the GST is that it is regressive, and therefore hurts the poor more than the rich. If this were true, the most efficient (ie utility maximizing) solution would be to just increase subsidizations for poverty (ie welfare).

The reason that the left doesn't like this approach is that it creates more transparency in the welfare process. That is, people can actually see how much subsidization others get.