Writing to the block should be expensive. But there won't be a problem because it'll only be used to settle Lightning Network transactions very infrequently, and could be massive amounts... not for small transactions.
Sure, but that’s a scenario where the usage of bitcoin is high and the total amount of money on tax fees is small compared to the market cap of bitcoin.
This means hash rate will be low compared to the market cap, and the necessary capital for a double spend attack may be worth it.
Maybe it’s all less of an issue because bitcoin will develop a network of trust that can replace the block chain.
But then, why not go with something like Stellar right away.
