tdryja
Altruism certainly exists, but assuming that altruistic actors (rather than self-interested actors) will expend more resources than attackers is a very different security model than what Bitcoin is designed upon.
Unfortunately Bitcoin has often been oversold as being "free"; but if transactions are free, and there's a fixed number of coins to mine, who pays for this whole network in 30 years?
The motivation behind the design of LN is to minimize the number of transactions which need to be globally verified (which has a cost) while still adhering to the general model of Bitcoin (decentralized, pseudonymous, etc).
You're right though that with tx fees being on the order of ~0.05 USD, you don't really need LN yet. I've long assumed that fees would become significant, pushing out some use cases. That's already happened with e.g satoshidice.
There are many problems which arise from unbounded transaction rates in Bitcoin. The most fundamental is that long term the coinbase reward is zero, and transaction fees are the only reason to create new blocks. Without artificial scarcity of block space (artificial in the sense of beyond what hardware can support) transaction fees would tend to zero, and mining would no longer generate revenue.
LN is proposed to allow many users and many transactions (when nodes cooperate) while keeping the security properties of Bitcoin (when nodes don't).