On the one side, besides the usual knee-jerk opposition to any kind of privatization and fearmongering about that foreigners might buy shares, there's the claim that we lose money by selling an asset that currently pays the government a dividend higher than the government's net borrowing costs. So if some SOE pays a 7% dividend to the government and the government's cost of borrowing is 5%, they reckon it makes more sense to keep the asset and to borrow money to cover shortfalls.Another issue which is getting much press is how much would the government get for the shares it would sell and what will it do with the money. A problem here is that talking about maximising the return from privatisation misses the whole point of privatisation which is to improve the efficient and productivity of the economy. If we just worry about how much we will get for the sale of assets then we should sell all of the state assets with the firms being monopolists. But that's unlikely to do much for welfare.
Forget SOEs for the moment. If any firm is providing a rate of return that seems to consistently be beating the market, we'd expect the stock price to rise until the rate of return falls into line with market norms, right? And if that doesn't happen, it's probably because there's something a bit nasty hiding in the risk profile. Now think about the SOEs. If they're earning a high return, it's either because their valuation is out of whack or because there's some risk. In the former case, the government can do well through an IPO - they'll get more for it than they thought it was worth. If instead it's just that the assets are risky, looking at the gap between funding costs and rate of return misses something a bit important.
Now, a reasonable counterargument is that the stock market rate of return is higher than the government's borrowing costs in general, so the asset price won't be bid up sufficiently to make the difference. But note two big problems. Sovereign debt from reasonable countries is safer than most stock market investments: the market index has to pay investors for the additional risk they take on. So selling a very safe asset (a bond) at a low interest rate while buying a riskier one (keeping an SOE) isn't a "Hey! Free Money!" deal. If it were, we'd also have proven that the government should borrow heavily on the international markets and buy up shares on the NZX. Most of us don't think that would work. So why do we think there's anything particularly special about the government's current set of asset holdings? If the argument for keeping Solid Energy in government hands is that the government's rate of return on coal investments is higher than its borrowing charges, then the government should also buy up any other firm providing a high enough expected return.
With partial private ownership of an SOE you run into the "a man can not serve two masters" problem. The aims of the private owners and the government are unlikely to be the same. Private investors will want to maximise profits while the government may well have political objectives it wants met. A firm can not do both and if it were to try it would just fail to achieve either.