That actually didn't happen in the Judas Contract itself. it was a few arcs later, after Perez left to do COIE. Within the Judas Contract itself, both are treated as villains and Slade is arrested.
I agree that Wolfman's attempting to write Slade as sympathetic and putting all the blame on Terra to the point that the Titans forgive him is batshit and poor writing, and precisely where the character went wrong. But I don't think Terra needing to be sympathetic is a "fact" at all, even if I prefer versions like the cartoon. They just shouldn't have overdone it in the aftermath by absolving Slade, they should have just left them both as bad people.