He is a dick, who used to be important for wikileaks but has kept tergeting specific angles for his leaks, which seems to indicate pushing a political agenda, which reduces trust in him and his platform.
The work he started is too important to leave in his care.
Example: During the DNC email leak, Wikileaks was clearly in a rush to publish the documents without removing credit card information and social security numbers, this is just sloppy.
Assange also worked to draw out the release of documents to increase Wikileaks publicity, this went on far enough that he publicly made announcements of releases that never came.
Wikileaks also published evidence that the DNC was behind the killing of Seth Rich, a DC staffer that Assange alluded to have given him the emails, this evidence came from a PI who has freely admitted not having seen any emails between Wikileaks and Seth not having seen the laptop containing the emails, or even having spoken with someone who had. The PI in question is a known FOX contributer.
Assange also seems to have weirdly close ties to Russia, he only had his morning talkshow broadcast on RT, supposedly they were the only ones to take up his show for syndication.
When he was first exiled, he requested that the Russian security service FSB should handle his security detail.
Today, the largest sponsor of Wikileaks is the Russian Government.
All of this speaks to Wikileaks not being the supreme beacon of free speach, but rather part of the Russian propaganda machine.
I don't think it started this way, Assange and Wikileaks probably started with the best of intentions, but the reality of our society came into play and Assange/Wikileaks sold thier credibillity for money from the Russian government.