That's not how most legal systems work. The prosecution is the one with the burden of proof. That said, for all I know, Assange may indeed be guilty. Perhaps we'll find out.
The OP was, as I understood it, not making a legal claim, but merely stating his opinion on whether or not what he is accused of did or did not happen. Proof on this position can come from both sides, but claiming that it must not have happened because the government is after him does not pass Ockham's razor.
I have to say, high profile person embarassing a lot of people... I'm a little more skeptical than usual. I'm not dumb enough to give him a free pass just because of who he is, but I'm sure as hell not defaulting to assuming guilt.
However - pitting women against enemies - either to seduce them or to just get them out of the way (via extortion) has happened before.