The "5 people" he tried to murder were illusory, it was in fact a single law enforcement agent on something of an entrapment run. (This information came out in the court transcripts a few days ago.) Law enforcement got Ross to believe there were people who had sensitive information about Silk Road staff and users - the type of information that, if released, would lead to: Ross going to prison, random users of SR going to prison, dealers on SR going to prison and believing Ross ratted them out, subsequently putting a hit out on Ross himself... imo, these hypothetical people who would blackmail to those ends, deserve to be in prison themselves. (And I think the law agrees.)
To be clear, I don't think it's acceptable to have citizens killing people, even if it's justified. But in judging the man you need to look at the circumstances. He wasn't a crazy guy shooting up a school. He wasn't going killing his wife so he can marry someone else. He wasn't killing a family member to collect life insurance. He wasn't killing a store clerk in the midst of a robbery. He was being faced with blackmail amounting to death threats. Putting out hits on the blackmailers was self-defense by proxy.