Parker versus NZIER on Capital Gains Taxes

Labour finance spokesperson, David Parker, sent this letter to the New Zealand Institute of Economic Research, regarding a report they wrote for Federated Farmers on Labour's proposed captial gains tax policy. 

I don't have time to read the original report or the earlier one by BERL referred to in the letter. What struck me, however, is that the points of disagreement are really quite tangential to the issues that should be at the heart of a debate on the merits of a capital gains tax (CGT). Let's take these in turn.

1. Parker believes the tax will raise more revenue than NZIER do. A CGT that is designed to ensure savings is directed to the most productive investments rather than be motivated by differential tax treatments is one that would raise zero revenue. Any CGT that increases revenue is one that increases the existing tax distortion penalising saving relative to consumption. Of course, one might have the objective of increasing the tax on saving for the equity objective of increasing the tax paid by the rich, but that is a different objective. Either claim the tax will raise revenue, or claim it is about encouraging productive investment, not both.
2. Parker believes the proposed CGT will be more progressive than NZIER do. This may be true, but if the objective is to increase the progressivity of the tax system, the policy question is whether it would be better to achieve this through increasing the income tax rates that would target high levels of wage and salary income as well, rather than just one component of capital income. 
3. Parker believes the current income-tax paid on trading is not important enough to make the claim that we currently have a CGT. That is possibly true, but it misses the point: We do have a perfect, all-of-the-advantages, none-of-the-disadvantages 13% CGT. It is called GST. 
4. Parker believes that a CGT will have more impact on housing speculation than NZIER. Again, this is possibly true, but why is that a good thing? Let's reiterate some points made previously, here and here: 
• Housing speculation is only profitable if house prices are expected to rise in the future. That is, speculation can't permanently increase house prices; it can only bring the increases forward in time. A policy designed to make speculation less profitable is a policy that admits that nothing will be done to curb the underlying drivers of house-price inflation. 
• To the extent that bringing forward future house price increases creates an incentive to build more houses, speculation will actually lower future prices. One can claim that the tax distortion that means home owners pay no income tax on the imputed rental they earn from themselves leads to a country having too large a housing stock, but not if your rhetoric is about making home ownership more affordable. 
• And curbing speculation in home ownership, to the extent that it has an impact on home affordability must operate through making renting more expensive. Again, this might be an objective, but not one that is easily squared with rhetoric concerned with poverty levels. 

One final point. Parker claims that the Australian experience is illustrative, because they had a CGT excluding the family home, their "home ownership rate was lower than New Zealand's. Now it is higher and ours is at a 60-year low". Is the claim that Australia's CGT had an impact on New Zealand's home-ownership rate? Or is this a difference-in-difference estimation that assumes as a control that Australia's rate would have fallen like New Zealand's but for the CGT?