Comment by crote
> there is no benefit for the user if it fails to to render some existing pages
What if the browser renders it incorrectly? If a corrupt tag combination leads to browser X parsing "<script>" as inline text but browser Y parsing it as a script tag, that could lead to serious security issues!
Blindly guessing at the original author's intent whenever you encounter buggy content is a recipe for disaster. Sometimes it is to the user's benefit to just refuse to render it.
and that's why HTML5 standardized the behavior, so both browsers will parse it the same, they just don't care if someone thinks it's "invalid" or not.