I'm generally trying to find drawbacks of this system, but not because I hate it. On the contrary; I just want to ensure that it'll remain.
i like how you think - don't ever take anything for granted and stay vigilant
While the block reward stills gives a fair amount of bitcoins, it won't do in one or two decades. The miners will have to arrange their business based on the transaction fees. And now I'm asking; how will the system work if we all move to the LN? Sure, by opening and closing channels we broadcast transactions to the main layer, but if the majority behaved just like how I did, the mempool won't ever full. If it doesn't full, there will be less competition of who will get their transaction confirmed first and thus, less fee. I'm afraid that, overtime, there will be less incentive which is also translated to less security.
the rewards will get smaller, but even if the rewards are small in the future, a bitcoin will be much more valuable than today (if everything goes as "planned"). it's hard to imagine what on satoshi will be worth when the rewards are really small
as other already have mentioned, the second layer is called the second layer cause the security of it depends on the first layer, there will always be an incentive also for second layer users to look out for the first layer if necessary