haberman's argument is making an assumption that perhaps you aren't. Namely, one of the benefits of Lua is that, barring behavior introduced by C extensions (and bugs in the Lua interpreter), it can't really harm your program. It can't crash or do anything else. It can suck up resources, but that's about it. As such, with whatever sandboxing you feel is appropriate, you can run arbitrary Lua code without worrying (e.g. World of Warcraft can run third-party addons). But with LuaJIT's FFI interface, it appears (note: I have never used LuaJIT or its FFI interface) that you can no longer trust arbitrary Lua because it can reach into your program and call whatever function it feels like, including the ability to crash you at random, or do other things that it's not supposed to be able to do. You can no longer just trust Lua code to not impact the rest of your program.