The ethical problem here is the consequence of the same game theory you're citing as a solution - the next country can always cut taxes more
If the US doesn't like Irelands tax policy ban US companies from setting up Irish subsidiaries.
A lot of this just comes down to the will of the people not being represented in their governments though, but thats just simply a bigger problem to deal with first before the cascade of other symptomatic issues of that root cause can be addressed.
When services that take care of people depend on taxes then yeah lower taxation without a backup is inherently unethical.
Additionally, lower government revenue should require cuts from other areas first, like military and corporate subsidies. We shouldn’t accept that any of the supposedly missing Apple tax revenue should affect the poor or uneducated. To threaten such seems unethical.
By the way, in case anyone claims that the tax revenue was 'stolen' from other countries- it's not up to the Irish government to charge higher taxes in order to subsidize other countries services (be it directly or by presenting itself as more expensive tax-wise than it needs to be).