While I get that it's better to be safe than sorry, it seems highly unlikely that anyone would even notice if someone were engaging in prostitution on SLS. If they were, it would more likely be reported by another member rather than being discovered by SLS staff directly, much less someone in law enforcement. If reported and SLS looked the other way, that would be a different matter.
I think it's also way over-estimated what SLS's accountability would be for someone using a legal impliment (i.e. SLS messaging) to commit a crime. It would almost be like holding Walmart accountable because someone bought a knife from them and used it to commit a crime. If Walmart sold them the knife suspecting the buyer planned to use it for a crime, that would be another matter.
While the letter of the law may hold SLS accountable, the spirit of the law should not. Of course some laws exist for the main purpose of revenue generation, so there is that. Just like the medical profession will base it's recommendations on the worst possible outcome regardless of how likely that outcome is, so will legal counsel. Everyone knows this is all about covering one's ass, which is one reason we can't have nice things ;-)

