IMO-—NO evidence should be withheld by the judge.
Yes, generally true. However, evidence may be precluded from admission as a sanction, for example, when a party has a duty to disclose it and does not. Additionally, evidence may be precluded where the probative value is outweighed by the risk of undue prejudice. Let's say hypothetically there is document that proves Grosskreutz is a member of the Nazi party. The probity of this is it may tend to show his tendency to incite insurrection, as he was doing on the evening in question. It has only minimal relevance on the issue of self defense, while it will allow the defense to highlight the attacker was a racist and not a crusader. A judge could easily decide that the Nazi party evidence is not admissible, not because it is irrelevant, but because it is unduly prejudicial with minimal probative value.