I can see that objection too, and it seems far more reasonable than assuming that soldered RAM automatically means a reduced lifespan machine.
But are Framework's RAM prices unreasonable? $400 for 64GB more of LPDDR5x seems OK. I haven't seen anybody object to Framework's RAM on those grounds.
With modular RAM, someone can buy old boards and RAM and use it for high-RAM applications down the line.
The workloads that people care most about today that need high RAM capacity are workloads that also need very high memory bandwidth. Old server hardware from eBay doesn't do a good job of satisfying the bandwidth side of things.