If they don't agree and can give you valid reasons why not, then you have little to worry about. DON'T think about this from a self-defensive point of view. Be open-minded about what they have to say. Remember, the odds are already against you. Be prepared for the worst.
Most people ARE closed-minded, no matter how much they disagree.
The messenger probably came into the relationship with you based on some biases passed on from the rumor source. So, don't be surprised when they give you supporting examples. Such are the characteristics of closed-minded people. The sooner you realize that, the better off you'll be. Don't dig yourself deeper by getting defensive.