Earlier quoted context omitted.
As a professing Christian, I would say your reading is correct, but this verse (like the rest of the ceremonial and judicial laws) is a command given specifically to Israel, not to all readers. Capital punishment is very common in this code of law, as it was in other civilizations from this time period. There are many laws that have to do with keeping sin and impurity/health risks out of the camp, and this is, by bib…
So why is it still there? I'm sure that at least some Abrahamic writings didn't get included in the Christian Bible. Or even in the Tanakh.
Why is it part of the Christian Canon? Because it provides important context for later material, e.g., Acts 15. The controversy in the early Christian Community over the application of the Jewish ritual law to gentile Christians is hard to understand without the Jewish ritual law.
Also, not all Christians are gentile Christians.