Re: What is the point
1) The ledger being shared is to keep the system honest. These nodes are simple, e.g. Raspberry PIs take care of that
2) Mining is to incentivise spread of the system. Miners take huge real economy risks to try and solve the sums first that leads to their single instance reward and then need to restart solving. Their cost in turn makes sure they use the cheapest energy available, so most mining is done near to alternative sources where there's an abundance that cannot be dialed down, like solar energy, earth warmth, wind and water. Coal is too expensive in most cases today, unless a government interested in bitcoin subsidizes it. Not many governments do... :)
Bitcoin was meant to take the place of the banking system. How much watts does the global banking system use, buildings, computer systems, security systems and infrastructure?
I believe at the moment bitcoin mining uses about as much energy as Las Vegas. What is the use of Las Vegas (in a global sense...)?
It's just a matter of looking at the picture with some distance, check facts and not hype and then to make your mind up. Bitcoin may not live up to all its early promises, but as a financial system that takes a crack at solving some big current financial uncertainty issues (indefinate inflation, excluding most of the worlds population to banking), it's a good start in my mind.