What would "solid proof" look like? Someone confessing? What if that person were paid off?
This is the problem with conspiracy theories: they are impossible to disprove to believers. Any evidence against them just serves to prove how deep the conspiracy goes.
At the moment, Seth Rich's death consists of a nighttime shooting, no killer caught, and nothing stolen. Police are treating it as a "presumed attempted robbery". If some local criminal is found with the murder weapon and no alibi, I think that would satisfy a lot of people that it was a robbery gone wrong.
Yes, there will be conspiracy theorists, but we're not really at "impossible to disprove" yet. There's still plenty of room for ordinary discussion - it's still an open investigation to the police even. I don't believe the 'revenge' story at all, but I don't think people are crazy for asking "Hey, what was Rich's DNC job? And is there evidence for the robbery story?"
"The DNC is rigged and Hillary Clinton is closely connected to many mysterious deaths." Conspiracy theorist!
leaks occur supporting the conspiracy theory
Look, the real issue here is that Assange is meddling with elections! Our corruption is our business alone! Look how he implies conspiracy theories (which we all know are never true). How reckless!!
http://www.nbcwashington.com/news/local/Man-Shot-Killed-in-N...
You've already jumped to "guy getting shot in DC because that shit happens sometimes" as merely a possibility that hasn't been completely ruled out.