We should believe it is true for now. Although the rule is innocent until proven guilty, when someone has the potential of being harmed it is better to err on the side of caution. Assange could be under a smear campaign but I want to hold out defending him for the benefit of the protection of a potential victim.
People rarely accuse someone of rape unless it is true. It is very hard to prove that they rape occured, because the burden of proof is on the victim. Many victims have been harrassed or punished for accusing someone of rape, especially if that person is well liked and well respected.
It is not possible for any of us to judge whether or not the allegation of rape against Julian Assange is true. That is a question for the courts to decide once they have reviewed the evidence. As in all cases, a person should be seen as innocent until proven guilty.
At this point, I do not think that I, or anyone else, can say if Julian Assange is guilty or not. These allegations need to be taken seriously, and he needs to be questioned. After an investigation, the truth will come out, and he needs to pay the consequences if he really did this.