While parents usually want what's best for their adult children when it comes to their relationships, some parents can't seem to trust that they raised a person who is capable of making their own decisions. Unless the partner your kid brings home is a living, breathing red flag of abuse or toxic behavior (like patting pizza), keeping your opinions to yourself is always the most peaceful approach.
If drama is unavoidable though, it can sting even more when your partner refuses to defend you while you take a constant string of hits from his mother who doesn't know she has a thunderous whisper. She can hear you, Linda!