The idea that SR and DPR was just an open experiment in pure market values for their own sake is kinda cute, but very mistaken. He made millions in the first online open air drug market in the world; how many other people in similar positions are pure idealists and nice people? There absolutely was an open weapons market that sprung off of SR (DPR, even as big a media whore as he was, recognized the potential for trouble at his flagship site). It didn't last very long because no one that belonged to the group trusted who they were talking to and the payments for amounts that high and all the shipping and security issues involved didn't leave anyone feeling comfortable about the idea, but it absolutely happened. And the emails talking about the torture and murder were found on his admin acct, which was absolutely and unequivocally tied to him in real life. In the email chain he also talked about hiring a hitman once before. There is less than zero reason to believe that was made up. I remember altoid coming to several forums I was a member of when SR first went live, telling everyone about 'this forum I just found' or, in at least one case I remember, openly telling us he had made it. He wasn't a nice guy then, and the fact they found him with millions in commision and still courting all the media attention possible speaks volumes about his character.
SR wasn't even close to the first of its kind. The only unique things about SR was how openly they were taunting the most powerful government in world history and how often they advertised. There have been places like SR since TOR and PGP became things, most of them are just far more careful. You can't forget how many laws you're flaunting and how severe the punishments can be for anyone that gets caught.
And if you think all that stuff is disallowed even on SR, I don't think you've gone very far down the Deep Web rabbit hole. Weapons were on SR at one point (only completely disallowed after the weapons site went live), and at least among vendors talk of snitching and violence wasn't uncommon. You don't participate at a high level in a place that makes that much money without potentially getting your hands dirty.