Gentle Readers: That it is acceptable to be rude so long as you provide a justification for your behavior is not, Miss Manners assures you, correct. But neither is it an unusual ploy.
Take the cases of a young lady who detests carrots, a young gentleman recently converted to vegetarianism out of concern for the planet, and an older gentleman with a life-threatening allergy to shellfish.
The older gentleman has spent a lifetime quietly avoiding shrimp cocktails. His friends and relatives know his situation and keep an eye out for him. But he must still wearily abide the rude dinner partner who insists on knowing why he is not eating the clam chowder, which she assures him is really delicious.
The young gentleman is passionate that it is everyone else, not himself, who is at fault: They are either unaware of the cruel and destructive nature of the meat industry, in which case he is doing a public service by educating them, or they are indifferent to it, which pales in comparison to anything he could say.
The young lady, though not yet 14 years of age, has already realized that it is simpler to tell everyone she meets that carrots send her into anaphylactic shock than to admit the truth, which is that she hates them.
The younger sufferers would be unhappy with the older gentleman's quiet acceptance. It is bad enough to have to navigate a dangerous world. Must the older man also spend a lifetime apologizing for something beyond his control? Or, as they would put it, apologizing for who he is? Injustice.
To Miss Manners' thinking, all three can benefit from her advice.
To the young lady: Dislike is not recognized as a medical condition, and falsely claiming it as such, while making your life easier, makes other peoples' lives harder. Your fib provides one more reason for callous hosts to dismiss assertions by people who really are in peril. Not being your mother, Miss Manners is not going to tell you to stop whining and eat your vegetables. But she is going to point out that you can push them to the side of the plate.
To the young gentleman: Rudeness is not justified by righteousness. Haranguing the other guests, who are just trying to have a pleasant evening, is not only rude, but will also fail to win you converts.
Gentle readers who thought Miss Manners was going to applaud the long-suffering older gentleman are only partly right. She can appreciate his thinking of others before he thinks of himself. But she rejects his belief that any prior discussion with a host with whom he sometimes dines, including, perhaps, an apology, would be rude. Nowadays, a good host will inquire and keep notes.
To the young pair who object that an apology is out of the question, Miss Manners answers, "grow up." The apology is not for the gentleman's condition, but for potentially inconveniencing his host. Being able to stomach the hypocrisy of making an apology without feeling overly contrite is a basic life skill to which no one can claim to be allergic.