could someone please explain to me why (apart from the potential torture aspect) it is so bad to share/discuss the concept?

There's a class of concepts called "information hazards." Like any other hazard, they're something that, if handled without care, will cause damage to someone. But with chemicals or lasers or falling rocks, you can stick up signs and people can stay out of the location where the chemicals or lasers or falling rocks are; putting up signs for concepts is hard, because warning signs can be easily self-defeating. If you label something a "horror story," all you're saying is "here be scariness." If you start talking about exactly why a story is scary, then you run the risk of giving people nightmares.

And so the Basilisk is disallowed for roughly the same reasons that shock images are disallowed. (This specific idea has given people nightmares, but the consensus is that it doesn't work as a serious proposal.)