X restricts what you can view without logging in. Many folks don't want to log in to X, for obvious reasons. Posting an xcancel link is kinda like folks posting various `archive` URLs to bypass paywalls, work around overloaded servers, etc. That's an extremely common practice here that usually goes without comment.

There's pedantic, and then there's needlessly pedantic.

xcancel is a valid workaround for X links on Hacker News and is sufficient for original attribution.