This argument resonates with me - but it's the same argument that has been made and artists have ignored or put up the same (unconvincing, in my opinion) arguments against the whole time. As you pointed out, this same discussion has been had every step of the way with digital art - from things like photoshop, to the tools that have been gradually introduced inside of photoshop and similar, to even things like brush packs, painting over kitbashes, etc. The traditionalist viewpoint holds strong, until the people arguing blink and realize everyone else eventually stopped caring and did what worked best for them.

At this point, I believe it's not a matter of intellectual honesty or actually disagreeing with any of it - it's just about outcomes. They don't want to see their work devalued, their sources of income drying up. It's an understandable fear. No one who enjoys the work they do enjoys the prospect of potentially having to change careers to keep making a living. Hell, most people that don't enjoy what they do have no desire to have to try and find a new career.

But humans are selfish. The same artists who are worried about technology taking their job will laud praise on technology in other areas that have eliminated jobs, with my recurring example being how happy they are for no longer having to pay a web dev to build them a portfolio site and can instead just go to squarespace and pay them a fraction of the cost. No one laments how there are basically no independent web designers building small sites anymore - it's just not a viable career. It's all been consolidated into shops working for big clients or pumping out themes for Wordpress, Squarespace, and Shopify. And of course, there are countless examples of this throughout history.

I'm not sure AI is going to be the great job destroyer we fear it is. I'm not sure it isn't, either. So I get it. This has a chance to force an issue on a massive scale that usually is much more limited in blast radius.

But to answer the question - I don't think it actually matters to them what the line is from any sort of rational perspective. It will move and shift based on the conversation to wherever they think it needs to be to protect themselves.

The main argument artists use isn’t that it is taking their job. The problem is that it was trained on their work without their consent and without compensation. This is fundamentally different from a Wordpress or squarespace and arguably different from models trained on open source software only.