You still need one slow and/or expensive Bitcoin transaction to start using it, while having enough funds for a justice transaction. You can't use it trustlessly on your phone and it's also not scalable (no decentralized route finding that scales exists and is an intractable problem).

Just use another crypto if you want to pay for things. 0-conf are just as instant as credit card payments are.

Doesn't relying on the Lightning network compromise Bitcoin's promise of no-trust finance?

Nope, you're still benefiting from the base layer's security while being able to transact much faster and cheaper on layer 2.