Bitcoin cannot be truly destroyed without a global catastrophe that wipes out pretty much all electricity on the planet. There are many things which could cause the value of Bitcoin to decrease, but it is nearly impossible for Bitcoin to be completely destroyed. In my opinion the way to hurt Bitcoin the most would be to buy an enormous amount and artificially sustain the price at ridiculous levels; get mining difficulty insanely high; and then unload your coins. If the market crashes enough miners will be unprofitable and shut down; causing blocks to not be processed.