Talking to kids about ethics?

My teen has the flu -- yesterday he had a pretty high fever. Today he's feeling better but still running about 100° and so he's still home from school. He wants to go "do something" because he's bored. But I also appreciate that being home sick really sucks.

He said he wanted to go to the donut shop and I said that if he was going to do that he needed to wear a mask so he wouldn't spread his virus around, that he can't go back to school until he's been fever free for 24 hours. He gave me this whole weird speech about how caring about other people is out and society has spoken -- we voted and we agreed that we're not doing that anymore. I just said that you have to base your morals on ethics on what you know to be true and not on what is in vogue and not what you know to be true.

Later when he was moaning about feeling awful again, I said "you can see why you don't want to spread this around, right? You don't want to give this virus to someone else, it sucks."

His response was "I get that you care about other people, but that's not really my thing. Unless I know you, you're just an NPC and I don't really believe that you exist or matter."

I honestly don't know how to respond to this kind of stuff. I feel like he's half just trying to get a rise out of me, it is still disorienting. Not for nothing I have no idea WTF he's been watching on his laptop all day but I'm sure it's a cesspool.

FWIW, he has an unusual history and, without getting into the specifics he was adopted as a pre-teen after time in foster care, I haven't been the one instilling him with a moral sensibility for his whole life. I think that might be why I want perspective. I definitely don't want or need a speech about how I raised him so this is all my fault.

But ...other parents of teens, do your kids say this kind of shit? How do you respond to it?