> most of the defenses of the RIAA's actions here don't make any sense.
HN is not a court of law, most people here are not lawyers, let alone well-paid and competent lawyers like the ones the RIAA can afford.
> wouldn't anybody making the tool then just not do that?
Sure - which is why you're not seeing many ads for tools to steal cars or pick locks. But it's not only about the way the material is promoted, it's also about how it's obtained, whether the seller could reasonably know what it would be used for, and a bunch of other stuff.
You can't look at this from a binary perspective; despite depictions in popular media, the law is typically not about "aha" moments, but rather about putting a number of coherent pieces together to paint a certain picture.
Moreover, that would save the law from being a dead letter in the sense that there would be circumstances when it could theoretically be enforced (i.e. when someone is overtly marketing it as a tool for infringement), but wouldn't anybody making the tool then just not do that? It's still exactly the same tool. And then what does the tool have to do with anything anyway, when what you really have is a law against speech promoting copyright infringement?