Not all thoughts are original.

Agreed, and I am also 100% opposed to SW patents. No matter what I wrote, if someone came up with the same idea on their own, and finds out about my implementation later, I absolutely do not expect them to credit me. In the use case you describe, I do not see a problem of using other people's work in a license breaking way. I do however see a waste of time - you have to triple check everything an LLM spits out - and energy (ref: MS trying to buy / restart a nuclear reactor to power their LLM hardware).

Further, whether I should be at fault for LLM vendors who may be breaking copyright law, is like trying to make a case for me being at fault for murder because I drive a car when car manufacturers lobby to the effect that people die more.

If you drive a car on "autopilot" and get someone killed, you are absolutely at fault for murder. Not in the legal sense, because fuck capitalism, but absolutely in the moral sense. Also, there's legal precedent in a different example: https://www.findlaw.com/legalblogs/criminal-defense/can-you-get-arrested-for-buying-stolen-goods/

If you unknowingly buy stolen (fenced) goods, if found out, you will have to return them to the rightful owner without getting your money back - that you would then have to try and get back from the vendor.

In the case of license agreements, you would still be participant to a license violation - and if you consider a piece of code that would be well-recognizable, just think about the following thought experiment:

Assume someone trained the LLM on some source code Disney uses for whatever. Your code gets autocompleted with that and you publish it, and Disney finds out about it. Do you honestly think that the evil motherfuckers at Disney would stop at anything short of having your head served on a silver platter?