I learned my lesson when I thought side-chains would kill altcoins.

They will. You'll learn your lesson again.

If they were going to do it they'd have done it already.

Nope. Both LN and side chains need segwit.

I'm not up on the latest maybe, but Liquid has been a working side-chain for years. Innit?

Liquid is a very specific case for a side chain. Can't be a true competitor.

Quote

Instead of proof of work (like in Bitcoin), Liquid depends on a distributed group of signatories, or functionaries, to create blocks.

So side chains secured through proof of work require SegWit?

No. Bitcoin needs segwit if side chains use it as base.