"That means guilty until proven innocent?"

No, it means that where someone is hitting someone else with a baseball bat, it can safely be assumed that they are not muttering sweet nothings and terms of endearment unless thay can show otherwise.

I muttered jealous oaths, and things,
As I punched him black and bluer,
Then I opens up this manhole cover
And I bungs him down a sewer.

From The Portuguese by ???

A case in point... few would take that song as vicious in intent, even though it has lines like "I don't like Portuguese in general, and in particular I didn't like him". Because in the UK for the last many years, no one has seriously discriminated against Iberians, and we can have jokes like Manuel in Fawlty Towers. But I suspect it could be seen very differently in the current climate in the USA.