Wow it's really hard to pin down a definition of Nihilism. Anyway, I always saw Nihilism as a view that nothing is meaningful, that everything means nothing. But not that nothing matters. If you have no meaning to ascribe value to anything or anyone, you wouldn't find meaning in unnecessary harm or discomfort to others, in a harm reduction mindset.
Hurting other people makes me unhappy, therefore I choose to try and make other people happy, because that makes me happy and I enjoy being happy.
Everything matters. Just because you cant see or feel dont foist it on those of us who can
True…
Needs clarification - nothing intrinsically matters. But things do matter to people.
You're conflating subjective and objective. Just because things subjectively matter to you (they also subjectively matter to most nihilists as well) doesn't mean they objectively matter. That's where the distinction lies.