This is a delicate question, because it takes a fair amount of knowledge, technical and historial, to appreciate the contributions of fundamental science to society as a whole. And even with some knowledge, this question of yours is a policial one, I would say a moral question. We can never know what will sprout out of the collaboration of thousands of scientists with various skills uniting their efforts towards one same goal, without monetary or personal gain as a reward. They just want to write one chapter, maybe one sentence or perhaps just one letter, in a universal book which is a legacy from one generation to another, and which an alien species could use to judge our value as intelligent beings. Because of this perspective, them physicists often want their single letter to be the most beautiful one in the book. So it's quite an amazing book in the end.
In fact, we can only rely on history to convey the importance of nourishing curiosity, almost as an art form which extracts us from our human condition. It may sound emphatic, but I truly believe that we cannot overemphasize this importance, despite the fact that a partial historical list is barely an acceptable argument, let alone convincing.
So here goes...
Time and again, fundamental discoveries first appeared completely useless. Take one of the first "research institutes" : Uraniborg where hundreds of people would work for Tycho Brahe to collect entire libraries of data on planetary orbits. They had to perfect the manufacturing processes of paper to write the results down (direct societal impact), and this data became crucial in establishing Kepler empirical laws, the seed for Newton's fundamental laws (very long term deep societal impact).
Take Faraday's quote when asked (by the ministry of finance) the practical value of electricity in 1850 : "One day sir, you may tax it".
Plank's discovery of the quanta from studying an anomaly in the theory for the spectrum of a oven (who would fund this research ?) leads to quantum mechanics, with innumerable consequences later enables solid states physics and the computers we converse with today. Take the development of internet protocols at CERN to exchange large amounts of data for statistical analysis...
Einstein's original work on relativity not being wildly recognized at first because considered to be too philosophical, eventually leading to nuclear weapons and power plants. Whether we favor their use or not, one must still recognize their essential social role. And there is much more to Einstein's work, the list would go on and on, everybody carrying a GPS in their pocket and not even buying a map anymore.
All medical imaging devices come from fundamental research in physics. The same community which builds high energy physics magnets are the only people able to develop the powerful superconducting magnets with such incredible uniformity that they enable us to picture the dynamics of neural processes (literally pictures at the level of brain cells).
The list goes on and on...
Without the support to fundamental research, our world would have been very different. We would always proceed by trial and error, pass to the next generation a bunch of unjustified traditions which would change several times per century, progress would be erratic and painstakingly slow. To escape this fate and Plato's cave is the value of the universal book. We should be grateful to sit on the shoulders of scientific giants, we should value natural curiosity as one of the defining traits of human societies. From the perspective of somebody embracing this moral, one should think of what happened during the last 150 years, accept that we cannot but assume our future role of ancestors and enable the world our descendants deserve.