You don't. Because you can't. Those illegal things are going to exist as long as there is a market for them. All you can do is ensure that the general public who doesn't wish to partake isn't exposed to it without looking.

Basically, you don't want your grandma finding the drug list or hacking tools unless she's specifically trying to find it. But it's going to exist, so let it exist (or rather, try if you wish but it's futile). Similar to tor hidden services and i2p eepsites.