If I break into someone's house to steal their drugs is it burglary? Or is it ok? Or would it depend on the judge?
It is illegal to break into the house even if you don't steal anything. It is illegal to steal the drugs even though the owner of the drugs possessed them unlawfully. So that's at least two crimes. On top of that, the thief will be committing the crime of illegal possession of a controlled substance after the theft.
There was a recent case reported in the U.K. where someone went to the police and complained a robber had taken his drugs. The robber was arrested. The complainant was arrested as well. One for robbery and possession of drugs, the other just for possession.
There will be cases where the police has problems finding evidence because the victim will not want to give evidence.