Subsidizing the cost of nascent "green" technology is needed to prod the industry to produce and learn how to make a better green mouse-trap through experience and R&D.
It's paying off now as electric cars are getting competitive. Gasoline engines have been the dominant car technology for a century, and thus have had a lot of R&D behind them. Thanks to subsidies to induce sales and R&D, electric cars have evolved to be competitive with gasoline.
Private companies rarely look more than 5 to 10 years ahead. It's why they have to be prodded via subsidies, etc. Finance theory on ROI teaches one to generally focus on the short-term. Whether this is entirely rational or not makes an interesting debate, but it's the ruling view of the current business world.
By the way, I consider "soft" socialism to be incentive-based. "Hard" socialism would be outright banning products. I'm generally against outright banning for products, such as incandescent bulbs and sugar-loaded Big Gulps. Tax them heavily as a disincentive, but don't ban them.