~400 transactions per block, 25 btc reward, ~500 usd / btc gives a transaction cost of 31 dollars each.
What happens to fees when mining rewards taper off? Just authoritatively stating "it'll be fixed" blindly pushes these problems into the future.
Sure. But if we don't need to worry about double spends, we wouldn't need Bitcoin in the first place. Bitcoin solves the double spend problem, which takes, roughly 60 minutes.
> Wait ten minutes for anonymous senders.
A single confirmation is not sufficient for large-value transfers. The larger the transfers the longer one should wait (up to about 6 confirmations).
A miner with, say, 5% of the global hashing power has a 5% chance of finding the next block. That means someone working with the miner has a 5% chance of successfully pulling off a 1-confirmation double spend. If I transfer 100,000 BTC to someone as payment for something, and the recipient delivers to me a product worth 100,000 BTC after one confirmation, then I have a 5% chance of successfully scamming someone of something worth 100,000 BTC (~$60M). That's an average profit per attempt of 5,000 BTC (~$3M).
If I instead wait, say, 7 confirmations (~65 minutes), the probability of pulling of a successful double spend with 5% of the network hash rate is around 0.000000078%. That's an average profit per attempt of $0.05.
If the blockchain is too heavy, why are miners willing to process transactions for tiny fees? Bitcoin creates a competitive market in transaction processing. If the blockchain becomes too heavy (as measured by the transaction fees miners demand), alternatives will arise or the protocol will be changed to stay competitive.