Bitcoin has already served it's purpose anyway. It already is a currency that people exchange for goods and other government issued currencies. It doesn't really metter what anyone thinks. Bitcoin has already succeeded. The only question that you need to ask is; Is it something you should invest in?
My personal answer? No. But who cares what I think. It's simply non productive, and frankly non-scientific, to stand up and say "Here's why bitcion is going to fail..." because it doesn't matter, it has already served its purpose.
The CPU cycles are contributing to global warming, and are a means for controlling the rate at which new coins are mined. Unless you have a large dedication to hardware tuning and a decent amount of real money, attempting to mine is of no use unless of course your heater is broken and you need your computer to keep you warm.