Second, if they were trying to be just a funnel but realised that they were only getting information from limited sources with a known agenda, then they would also know that they are facilitating a political agenda. They could be open about this. But they are not. They are keeping critical details of their own activities secret (ie they choose to be selective), which is directly contrary to their stated philosophy.
In a more empirical sense, an organisation can only be judged by its output, not by its slogans or cheerleaders. In that sense Wikileaks is clearly an organisation promoting a political agenda.
Yes, but that opinion is that powerful, unaccountable organizations shouldn't be able to keep deep secrets from the general public when they do things like manufacturing consent for war.
Being open about sources defeats the whole purpose.
So given that they can't select the sources, the claims of them being "selective" just sound ignorant to anyone who knows how they operate, especially when those same claims are so often repeated in publications which are openly selective.