Then all businesses should get the same deal.
Any business building a factory in another state goes through this, not just Tesla. For example, Boeing -- WA started to tax them out of existence and NC said: "Come over here."
I don't see the problem. This is capitalism 101 -- Elon Musk wants the absolute best deal for his company -- he has already proven that he can build a better mouse trap -- his electric car is faster than a 12 cylinder Aston Martin, cheaper than an Aston, with 260+ mile range (farther than an Aston) on a single charge.(*) His challenge is to sustain the interest -- he's got a lot of dragons to slay -- the entrenched car manufacturers, the oil industry, the car dealers' association, to name but a few.
Tesla would not be in the position of needing a gigafactory if it were not selling cars. Right now, the waiting list for a new Tesla is 4 months.
His Tesla cars sell, whereas the Volt does not. States are tripping over themselves to woo his gigafactory to their boarders -- the added revenue from those 6,500 employees -- housing -- food --- etc, etc is quite significant.
(*) Current record on the Telsa Model S is approx 500 miles on a single charge.