The rebates and tax cuts are working as intended. For example, by paying $7,500 for a certain class of electric vehicle, we tip the balance for people considering buying a somewhat less expensive internal combustion car. Just by tipping the scales, we shift a significant fraction of the demand from IC to electric, which makes a huge difference in the market, and therefore capital investment in manufacturing. Just doing this for a few years gets us decades ahead of where we would be in terms of electric vehicle technology.
Corruption is always possible but it's not a given. For an old rebuttal, Musk's "The House Always Wins" essay still applies. https://www.tesla.com/blog/house-always-wins
P.S. The tax credit already get phased out above 200,000 vehicles per manufacturer, so it's not going to apply to all 500,000 pre-orders (even assuming they all become sales). https://energy.gov/eere/electricvehicles/electric-vehicles-t...