Though they’re no longer ugly, impossibly expensive and impractical, electric vehicles need to out-innovate fossil fuels if they are ever to displace the internal combustion engine.

Skepticism of electric cars melts a bit more with each new announcement from the likes of Tesla, which last week launched production of a mass-market vehicle, and Volvo, which days later promised to phase out gasoline-only engines by 2019.

But that progress comes with two big caveats: First, it has relied on extensive public subsidies and, second, it has done little to reduce planet-warming emissions of carbon dioxide. If electric cars are ever to displace gasoline engines without government putting its thumb on the scale, they must not only keep innovating but outrun fossil fuels where productivity also keeps advancing.

The federal government offers a tax credit of up to $7,500 each for the first 200,000 electric or plug-in hybrid cars a manufacturer sells. Throw in state tax credits, subsidies for recharging infrastructure, relief from gasoline taxes, preferential lanes and parking spots and government fleet purchases, and taxpayers help pay for every electric car on the road.

What happens when the credits go away? When Hong Kong slashed a tax break worth roughly $55,000 for a Tesla in April, its sales ground to a halt. In Georgia, electric vehicle sales plummeted 80% the month after a $5,000 tax credit was repealed.