You've all heard the environmental/waste argument "the Bitcoin network uses too much computing power."

Right now I don't think this is a good argument. We're not spending that many resources mining if you make the comparison with the cost of securing banks and credit cards. However, if bitcoins jump in price like a lot of us hope they will, this will be a legitimate problem.

Imagine that the price of BTC reached $1,000,000 USD on January of 2016. The block reward will still be 25 BTC, meaning that every day, 3.6 billion dollars worth of bitcoins is distributed to miners. Miners would be expected to spend almost 3.6 billion dollars per day to mine these coins. That's 1.3 trillion dollars per year, or almost 2% of the wealth produced globally every year (as of right now).

Of course in this situation, the Bitcoin network will be very widely used and worth protecting from attacks. The question is: is 2% of global wealth devoted to protecting the Bitcoin network overkill? Maybe it would have enough protection with just 1% of global wealth, or even 0.2%.

The general problem is that the rewards to miners will be somewhat arbitrary and not calibrated to the security needs of the network, because they're based on parameters that Satoshi picked before he knew what the adoption/price curve would look like.