Open source software is published to the world and used far beyond any single community where certain norms might apply.

If you care about what people do with your code, you should put it in the license. To the extent that unwritten norms exist, it's unfair to expect strangers in different parts of the world to know what they are, and it's likely unenforceable.

This recently came up for the GPLv2 license, where Linus Torvalds and the Software Freedom Conservancy disagree about how it should be interpreted, and there's apparently a judge that agrees with Linus:

https://mastodon.social/@torvalds@social.kernel.org/11577678...