I've run into one too many fics where no one understands and accepts Rodney like John does. Which is, of course, why Elizabeth recruited him for the Atlantis expedition, worked with him in close quarters in Antarctica for months, if not more than a year, and then brought him with her on a potentially one-way trip with only a couple hundred people to act as a buffer between her and her head scientist whom she would have to see on a continual basis. Because she knew that only John would be able to revel in Rodney's Rodney-ness. Even though they hadn't met John at that point in time. She just knew.

Elizabeth and Rodney. They're pals. He wrote a 500 page biography. Of her! He could have spent his time with superpowers doing anything, and he made sure to write five hundred pages to try and make everyone see her the way he did.

Which is to say that clearly there are plenty of people on the expedition who can accept Rodney, even with his flaws, and who have from the very start. And people who call him on his mistakes! (Which is okay, and not a sign that he needs to consume an entire lemon chicken stir fry dish, a la some fics out there.) So why should it only be one person who does?