On the scalability issues of onboarding millions of LN mobile clients

In a recent email conversation on the bitcoin-dev mailing list, Lloyd Fournier asked why it's necessary to run a full node in the Bitcoin network. Luke Dashjr replied that it is necessary for security purposes, as the trust-minimization of Bitcoin security model relies first and foremost on running a full node. If users don't verify their incoming transactions properly, it can compromise Bitcoin's security, which depends on the assumption that a supermajority of the economy is verifying their incoming transactions using their own full node. The problem arises when a large part of the ecosystem gets scammed at once, resulting in an attack happening in practice. For example, if bitcoin had 10,000 users, and only 10 of them use a full node wallet while the other 9,990 use an SPV wallet, then if a miner attacked the system by printing infinite bitcoins and spending coins without a valid signature, the 9,990 SPV wallets would accept those fake coins as payment. After some time, those coins would likely be the ancestors of most active coins in the 9,990-SPV-wallet ecosystem, causing Bitcoin to split into two currencies: full-node-coin and SPV-coin.The fraud miners may become well-known and published on bitcoin news portals, but the 9,990-SPV-wallet ecosystem has a strong incentive to be against any rollback. Their recent transactions would disappear, and they'd lose money. They'd argue that they've already been using the coin for a while, and it works perfectly fine. The SPV-wallet community might even decide to use something like invalidateblock to make sure their SPV-coin doesn't get reorg'd out of existence, and there'd also likely be a social attack, with every bitcoin community portal being flooded with bots and shills advocating the merits of SPV-coin. This is not a hypothetical scenario because we already saw the same thing during the scalability conflict 2015-2017.In conclusion, it's necessary to run a full node for Bitcoin security purposes, and if a large part of the ecosystem gets scammed at once, it can have disastrous consequences resulting in Bitcoin splitting into two currencies: full-node-coin and SPV-coin.