> If I give a company $100M in tax breaks to come to my city, and they end up paying $50M in tax (instead of $150M), the outcome was financially positive as the alternative was that they don’t come and my tax revenue is $0.
The issue is that this is true of every company. It's much more efficient (and fair) to just have a lower tax rate to begin with and allow that to attract businesses in general than to negotiate with each of them individually and screw over any that aren't big enough to get that level of attention.
Also the broken window fallacy: yes the money will have had a positive effect, but was this the best effect that could be achieved with the funds? Maybe it brought a company and a few jobs but the same funds could have increased local pensions, increased teacher training or built a new wind energy installation.
The question is not "was this a useful use of money", it's "was this one of the better/the best use of these funds".
Not if attracting the company is still net positive, i.e. they're still at least paying for the services they directly consume. Lowering the "net profit" from taxes on a company that otherwise wouldn't be in your jurisdiction doesn't cost you anything. There is nothing you could have otherwise spent the money on because there otherwise wouldn't have been any money to spend. At best you only lose a small amount by letting them leave.
But if you can get any gain at all then why is it being done for only one company rather than in general as a matter of policy?
The issue is that this is true of every company. It's much more efficient (and fair) to just have a lower tax rate to begin with and allow that to attract businesses in general than to negotiate with each of them individually and screw over any that aren't big enough to get that level of attention.