What is the point in preventing use of fossil fuels?

What is even the point of trying to prevent the use of fossil fuels in order to prevent global warming? This argument assumes an unlimited quantity of quality fossil fuels available (quality= the amount of energy it takes to obtain in comparison with the energy it gives, eg crude oil had a ratio surplus:extraction expense of 100:1 in 1930, now it is 3:1). If the world has pretty much hit peak oil, there is no way that the quality oil left isn't going to be extracted by someone. Shouldn't the effort be channeled into ways of limiting the predicament outcomes?