Tybalt is portrayed as a villain in the play, and yet his death is not a positive event. Why is Tybalt's death bad for Romeo and Juliet?

Although Tybalt is a villain, he is still a cousin of Juliet's, and after their marriage, he is then related to Romeo as well.  Besides being officially "family," there had recently been made a law in Verona that no one is to fight between the two families.  Anyone who is caught fighting will be punished by death.  The Prince announced that, and all of them knew the consequences.  When Romeo is banished, the two lovers cannot be together.  This is what begins the confusion.  They no longer can communicate and rely on others to get messages back and forth.  That is what causes both deaths to occur in the end.  Had Tybalt lived, Romeo never would have been banished, and they would have been able to announce their love/marriage to their families.