Should she invite warring guests to her party?

Dear Aunt Dandelion,

My birthday is coming up and I'm hosting a small dinner party. I've invited eight of my friends, including my brother. Unfortunately my brother hates one of my good friends, and has told me that he won't come to my birthday if she is invited as well. I'm not quite sure why he dislikes her. He organizes camping trips, and I think that she complained to other people about one of his trips, how expensive it was, and that he was possibly making money off of it. Anyway, my brother says that if I invite her, I'm being disloyal to him. What do you think? Is he acting childish, or does he have a point? What if this was my wedding? I can't not invite people just because others may hate them. This is my birthday, don't I have the right to chose whom I invite? -- Confused Birthday Girl

Aunt Dandelion answers: 

Your brother sounds very childish indeed. If all your guests adopt gracious manners for the duration of the dinner, such a petty problem would be overlooked for the sake of a harmonious evening. Etiquette is a means of putting on a veneer of politeness and diplomacy in a social situation.

However, as hostess, it is your duty to compose your party of guests who you feel will be interesting to each other and will mesh well. Since you know in advance that your brother is not going to put aside his feelings, I suggest you leave him out of the dinner party to avoid unpleasantness and embarrassment for your other guests. Perhaps you can have a separate celebration at home for family only.