[ethn]

Beyond what olegkikin mentions, the Lightning Network requires you to put stake (the total amount of bitcoin that can be used within those off-chain transactions). The illiquidity opportunity costs of that stake is greater than any value that the LN provides. There's a reason why we don't use pawn shops to buy groceries every week. Further, there isn't really a use case where you want to put some money at stake to do some transactions really quickly. Also, as Nakamoto† mentioned before, you can determine if a transaction is valid with very high probabilistic guarantee within a few seconds (with less risk than credit cards) without any change to the current network.

If for some reason you don't believe that, then there will always exist credit card companies that could provide instant transactions with guarantee as a middle man. Alternatively, there exists solutions like BitNotes.

†https://bitcointalk.org/index.php?topic=423.msg3819#msg3819