

“Drawing the line” is a Thought Terminating Phrase, which is a concept worth reading and thinking about.
In the abstract / in your example, if you’re just “drawing the line” then no, that’s not a legitimate argument. It is literally just you saying “nope, I arbitrarily say this is different then this”.
However, if you can back up why one thing is different from the other, then it is valid to distinguish between them. Sometimes it can be worth dividing a system into chunks and drawing arbitrary lines rather not drawing any, but you should still be able to logically back up why it’s better to chunk things than not.
But in your example, it sounds like you don’t actually have a logical argument, just one based on you arbitrarily deciding that music can only be made by a human.

The entirety of your argument boils down to you arbitrarily deciding that music needs to derive from human intentionality.
That’s not an actual argument about whether or not AI is capable of creating music, that’s you redefining music to make sure the answer is no.