Just that we're in a mining bubble and the miners of today are likely to go bust in a few years as the block reward drops off and people switch to zero fee lightning.
I've never understood this one.
For lightning channels to open and close they have to have on chain transactions. If we assume blocks remain small then on chain transactions will be hideously expensive. Miners will make more money than ever in fees.
Maybe there'll be a yet to be discovered way for channels to never have to go on chain again, but there'll always be on chain needs.