That's fair 0x83F1, that would be a valid attack. The economic incentive for that attack is pretty low (unless Chain is working with miners to boost their fees)

That's fair 0x83F1, that would be a valid attack. The economic incentive for that attack is pretty low (unless Chain is working with miners to boost their fees), but I see your point, you are definitely giving up some level of security and the trustless nature of Bitcoin by using an API for sure. I do think as the Bitcoin ecosystem grows, it's going to be inevitable that some tradeoffs are made for usability, convenience and extensibility by mainstream users. I would be most worried about any tradeoff that was both a) open to a technical attack vector b) created economic incentives for parties to be malicious. Situations with only a) or b) but not both will likely be tolerated by users and only reinvented when major issues arise.