Party spokesperson: The opposition party’s proposal to stimulate economic activity in the province by refunding $600 million in provincial taxes to taxpayers, who could be expected to spend the money, envisions an illusory benefit.
Main Conclusion
The proposal to stimulate economic activity by refunding $600 million envisions an illusory benefit.
Intermediate Conclusion (So)
Either the province's taxpayers or its workers, who are also province residents, will have the $600 million to spend, but there will be no resulting net increase in spending to stimulate the economy.
Evidence (since)
The budget has to be balanced, so there would either be new taxes needed (defeating the purpose of the refund) or the province would have to lay-off some of its workers (also bad for the economy).
Evaluate
If I were trying to describe how the author reached her conclusion, I would probably call this a "Damned if you do, damned if you don't" kind of argument (i.e. "Either way you slice it, it's still bad").
The author tries to show that a plan won't achieve its intended result by introducing considerations that make it seem like whether we go down Road A or Road B, we won't reach our destination.
Goal
We just want whichever answer choice we can match up to the specifics of this conversation.