If a subsidy is given to a second best solution then that subsidy is first not as efficient as it could be but worse still, it may by capturing some benefits impair on the viability of the best solution.
Let me try to explain it as easy as possible
Suppose we have an environmental project that carries with it a total of 10 green points of possible environmental improvement and that, one approach, the best, could catch 7 of these points for 7 dollars of investment while, the second approach, the second best, can only catch 5 points and requires a 6 dollar investment.
If then for any reason, such as undue lobbying, it is decided to go ahead with the second best approach then 6 dollars would have been invested in order to capture 5 points, not too bad.
But let us suppose both approaches were only able to capture the same type of seven points and three points could not technically be captured by any approach, then we are left with only 2 points to catch at a 7 dollar cost… meaning that these 2 green points will never be captured.
Should that be of concern to us? You bet! Besides the differences in environmental efficiency of what is out there is mindboggling. Solar voltaic panels and hybrid cars should perhaps even be prohibited as they represent truly expensive green placebos.