My reasoning:
* Each transaction in Bitcoin costs hundreds of time more than a credit card transaction to process. (currently this is subsidized by inflow of capital into the eco-system, so users haven't felt the full effect).

* Hundreds of millions of dollars are paid to mining hardware vendor and electricity company. This will continue year after year, and only will grow more and more as Bitcoin grows bigger. The Bitcoin community is being bled dry. The price action this year shows that even with massive amount of big name adoption and good news, the inflow of capital is having trouble to keep up with the insane surge of mining cost.

* There are better ways to secure the network, for example Bitshares's DPoS system or ETH's upcoming PoS system. Money is re-invested into the eco-system and community, instead of paid to hardware vendor and electric company.