No, the opposite, it's worse to detain a diplomat. International law (to whatever extent it exists) cares very little for one's standing as a politician, but a great deal about one's standing as a diplomat.
Note also: you have to be accepted by your host country to be immune from their laws. Diplomats are not a class of people above the law. The US isn't compelled to recognize immunity for anyone until it (for instance) admits them on their diplomatic passport.
It's hard to imagine any circumstance in which diplomatic immunity in the US could come to play for Julian Assange, no matter how wacky Australian politics ever get.
Note also: you have to be accepted by your host country to be immune from their laws. Diplomats are not a class of people above the law. The US isn't compelled to recognize immunity for anyone until it (for instance) admits them on their diplomatic passport.
It's hard to imagine any circumstance in which diplomatic immunity in the US could come to play for Julian Assange, no matter how wacky Australian politics ever get.