I’m not the other person, but I think you might be confusing the term “determinism.” I think you might also have a bit of an over-enthusiastic understanding of quantum mechanics, which is a very common problem when people have QM explained in lay person terms I’m not going to get into the QM stuff because I’m a biologist and not a physicist, and I think your world just became more interesting with your new information. I’d just say hold off on the conclusions until you read a bit more, and start sliding towards the actual science books rather than the pop science books as you get your feet under you. You’ll have a different appreciation once you can read an advanced undergraduate textbook on modern physics.
Determinism as used here means behavioral determinism. There is significant evidence that a large number of our actions and reactions aren’t thought through, but rather are “automatic” responses. In fact, some neuroimaging work on decision-making has indicated that we reach a conclusion and then reverse-justify it by thinking we’re thinking about it. My subconscious mind has already decided to buy the bagel, but my conscious mind is still talking itself into it.
Again, people can take that kind of thing to an unjustified extreme. I think free will exists in a limited sense, but that it is highly constrained. In this case (the original question, not the person to whom you’re replying) is using their own misunderstanding of behavioral determinism to excuse their misbehavior. It’s a self-indulgent philosophy that you can probably pick apart if you really wanted to spend the time and effort in making them meticulously explain every step and aspect of their position, but it’s probably easier to just drop the person or to deal with them while remembering they’re possibly clinically psychotic, but almost definitely at least an asshole.