Re: Seems to me ...
"like the only long term sustainable corporate tax rate is zero."
Not really. Look at it like this:
You're running the tax system for a country.
First of all, as another commentator has noted, zero corp tax allows anyone who can incorporate to pay no tax at all by doing so and thus avoiding income tax. So now you have to pick between high and low strategies.
Divide your potential tax base between local and multinationals. Local businesses have no option but to pay CT. Multinationals can choose and your strategy will determine what they do.
If you have a small country with a small* local tax base charging a high rate on not very much yields not very much from your local tax base. Charging a lower rate yields less but that's less than not very much so you're not losing a lot. But if your lower rate brings in a foreign corporation or two you're getting a low rate on humungously much which adds up to doing quite nicely in relation to your needs and your local businesses are also happy because they're not paying as much.
If you have a large country with a lot of of local businesses you still have the possibility of attracting multinationals by a lower tax rate but the gains of that risk being less than the loss of tax from the local businesses. You could also get involved in a race to the bottom which is of advantage to the multinationals and no-one else. You maximise your tax take by screwing as much as you can from the local tax base and let the multinationals go elsewhere.
People keep posting here saying that the Irish tax rates are screwing the Irish tax payers. They're not. They're indirectly screwing the US tax payers.
*Small in relation to the potential multinational tax base.