Checks, debit, cash, & bank wires are like #lightning, #liquid, ecash, & other Bitcoin scaling layers. The layers are good for privacy. There is no reason to use a different monetary token & deal with exchange costs & risks & lack of acceptance.
All you quoted about bitcoin layers can still be tracked and also needs a lot of money to be staked by rich people or pools (i thought you would actually quote dark web bitcoin mixers), bitcoin will be traced to KYC and it will be divided into controlled accepted coins and unregulated coins. At this time, BTC blockchain is coded to show all sats backway to their mining. Bitcoin has become an institution and all its thoughts are traced to austrian economy (not quoting that hayek would want to have concurrency in different coins). Thats totally different to monero, which was created as a TAZ (transitory autonomous zone) by cryptoanarchists, not meant to be a institution neither the only one used. It is meant to be used by the ones that want and need privacy. Would not be great for economy at all to bitcoin be full privacy as monero is.
Bitcoin is always going to show a clear path back to issuance, that's how triple entry accounting works & is one of the key innovations we need to prevent inflation & counterfeiting. Some of the richest people in bitcoin are anonymous cypherpunks who quietly go about their lives. Providing liquidity for more private payment layers helps them as much as it helps others. Privacy is still possible with traceable base layer txns. Moving money through other layers breaks the clear link to ownership onchain.
Being private AND offchain is definitely ideal for privacy. That is true. Monero gets L2s with FCMP++ in a year or so. "There is no reason to use a different monetary token & deal with exchange costs & risks & lack of acceptance." What? You deal with exchange costs and risks in lightning, liquid, and ecash too. You also deal with the additional cost of force closure fees in lightning, and rug risk with ecash. Liquid rug is also possible too just much less likely (privacy sucks though. doesn't hide sender/receiver and abysmal anon set). https://boltz.exchange/
Why use Monero's future L2 if blocksize is dynamic & can adjust to any demand? There is no exchange risk when swapping between BTC tokens. Liquid to LN swaps happen in the background when you make a txn from a wallet. So if someone doesn't support Liquid they get a LN payment instead. There will be similar bridges to everything else & LN forced closes will mostly be LSP problems, not average consumer level issues.
Same reasons you use an L2 on Bitcoin. You would use L2s on Monero for instant and much cheaper payments. Offchain txs can also be better for privacy especially when combined with an encrypted base layer. There doesn't have to be exchange risk with Monero either. There are several atomic swaps out there between BTC and XMR like UnstoppableSwap, BasicSwapDEX, and soon Serai if that is what you meant. You can have wallets that do the exact same thing in the background. Cake and Stack already do this. Ok sure, but you're only getting around force closes this way by taking on intermediaries like LSPs meaning you're asking permission to transact and introducing privacy implications.