There's nothing wrong with offering an alternative language or even with basing another language's compiler on javac. What's wrong is the misrepresentation of what they're doing and how they try to hide the technical risks involved from their users. Don't call yourself a Java library if you're really a different language that's very much not Java; don't say you're a compiler extension if you bypass the compiler extension API and change its internals to turn it into a compiler for your new language. Their choices are fine; telling users you've chosen something else is not.