First, look at it from the standpoint of the economic burden on a business. I run a business. I have to file my GST input credits and returns. I'm doing the same amount of work to file for 5% as 7%.
That means, similarly I would presume--this is pure conjecture--the Department of Finance is going to have overhead costs in a similar range. So, in effect, by reducing the GST from 7% to 5%, they have effectively reduced the efficiency of the collection, which is not necessarily the best signal, I would think, to send businesses about improving productivity when the department is heading in the opposite direction itself.
Second, there is quite a bit of evidence from the OECD, from the Department of Finance--I gathered this information from a report of the Fraser Institute about the effectiveness of various revenue-neutral forms of taxation--and consistently, consumption taxation was one of the most effective forms of economic stimulation and economic benefits derived from that form of taxation.
It seems to me if you have a revenue-neutral situation, you have more personal income with reduced personal income tax, and then you have the choice of spending on consumption or investing and reinvesting in our economy. So there's the added benefit to that.
I'm not an economist, so I can't break down all the benefits that were identified in those studies, but that's my point of view.