Couldn't you say that about any off-chain protocol -- even Lightning -- since they aren't Bitcoin, and don't improve its on-chain throughput?
If Liquid is cheap, fast, decently secure and interoperable with Bitcoin, that seems like a good thing for Bitcoin and its users.
It's more about the centralized aspect of Liquid. I can spin up a Lightning node and connect to others and start using Lightning without begging anyone for access to the network. In order to get access to Liquid you need to go to a central entity and beg them to sell you LBTC, and hope that you will be able to convert it back to Bitcoin at a later stage.
I can't recall what 'Bitcoiner' it was, but Liquid was advertised as a scaling solution for Bitcoin, which is retarded because that's not the case at all. The point basically was that Bitcoin itself is slow and expensive, but Liquid fixes that problem. Conflict of interest it reeks of.
The narrative keeps changing..... Bitcoin's goal was to end middlemen services, and what are we doing? Yeah, introduce more of them.