Ah, the "externalities" trope.
Your imagined, unrealized externalities of the future may indeed be dire, but that has nothing to do with whether cheap energy is a good thing.
Let's, for a moment, imagine a dire, future externality of solar power - say the ivanpah generator, reflecting into space, attracts a violent alien civilization that comes and eats 90% of our population. Are you happy to pad the pockets of solar executives at the expense of the future?
Now, maybe if you had concrete, actual, real "externalities" that were paid by "all of us", like say, solar subsidies for bird zapping solar plants in nevada, or regulations that raised the cost of energy paid by "all of us", you'd have a case to make...but imaginary harms in some hypothetical future with tenuous attribution hardly make for good economics.