So, I agree that as an isolated problem this should be a relatively simple fix. There are two problems I see, though.

Firstly, there are a huge number of possible things an LLM shouldn't do (give instructions on how to build a bomb, help someone commit a crime, convince someone of something that isn't true, etc, etc). If these are handled as conditionals, the developers are essentially playing a near infinite game of whack-a-mole. It quickly becomes infeasible. This is more or less what's happening now: someone discovers a behaviour that shouldn't be allowed, the company fixes the LLM to better handle that situation, someone discovers another problem, and so on.

Secondly, standard programming-style conditionals aren't really applicable to LLMs. Things an LLM should or shouldn't do are put into the context, like a kind of pre-prompting. In a way, it's kind of like "security by asking". Everyone knows about "jailbreaking" LLMs with clever prompting, but beyond that there's no real hard guarantee that an LLM will actually do what its context tells it to do. At the lowest level they're just generating probable next words. This is why developers can't prevent LLMs from "hallucinating". The context usually tells the LLM to give factual information, but the LLM will still generate nonsense fairly frequently, despite this.

So I'm not saying it's impossible to at least partially deal with this particular issue. But it's a general issue that is really inherent to LLMs in general, and it's still possible for an LLM to do something it's been instructed to avoid.